Background Image-guided procedures for treatment of liver diseases can be painful and require heavy sedation of the patient. Local-regional nerve blocks improve pain control and reduce oversedation risks, but there are no documented liver-specific nerve blocks. Purpose To develop a safe and technically simple liver-specific nerve block. Materials and Methods Between March 2017 and October 2019, three cadavers were dissected to evaluate the hepatic hilar anatomy. The hepatic hilar nerves were targeted with transhepatic placement of a needle adjacent to the main portal vein, under US guidance, and evaluated with use of an injection of methylene blue. A hepatic nerve block, using similar technique and 0.25% bupivacaine, was offered to patients undergoing liver tumoral ablation. In a prospective pilot study, 12 patients who received the nerve block were compared with a control group regarding complications, safety, pain scores, and intraoperative opioid requirement. Student t tests were used to compare the groups' characteristics, and Mann-Whitney U tests were used for the measured outcomes. Results Cadaver results confirmed that the hepatic nerves coursing in the hepatic hilum can be targeted with US for injection of anesthetic agents, with adequate spread of injected methylene blue around the nerves in the hepatic hilar perivascular space. The 12 participants (mean age ± standard deviation, 66 years ± 13; eight men) who received a hepatic hilar block before liver thermal ablations demonstrated reduced pain compared with a control group of 12 participants (mean age, 63 years ± 15; eight men) who received only intravenous sedation. Participants who received the nerve block had a lower mean visual analog scale score for pain than the control group (3.9 ± 2.4 vs 7.0 ± 2.8, respectively; P = .01) and decreased need for intraprocedural fentanyl (mean dose, 152 μg ± 78.0 vs 235.4 μg ± 58.2, respectively; P = .01). No major complications occurred in the hepatic hilar nerve block group. Conclusion A dedicated hepatic hilar nerve block with 0.25% bupivacaine can be safely performed to provide anesthesia during liver tumoral ablation. © RSNA, 2021.

Spurred by current research policy, we are witnessing a significant growth in the number of studies that observe and describe sexual diversities in human physiology and sex prevalence in a large number of pathologies. Yet we are far from the comprehension of the mechanisms underpinning these differences, which are the result of a long evolutionary history. This Essay is meant to underline female reproductive function as a driver for the positive selection of the specific physiological features that explain male and female differential susceptibility to diseases and metabolic disturbances, in particular. A clear understanding of the causes underlying sexual dimorphisms in the physio-pathology is crucial for precision medicine.

Acetaminophen (APAP) is widely used as an analgesic and antipyretic agent, but it may induce acute liver injury at high doses. Alzheimer's disease patients, while treated with acetylcholinesterase inhibitor (AChEI), may take APAP when they suffer from cold or pain. It is generally recognized that inhibiting acetylcholinesterase activity may also result in liver injury. To clarify whether AChEI could deteriorate or attenuate APAP hepatotoxicity, the effects of AChEI on APAP hepatotoxicity were investigated. Male C57BL/6J mice were administrated with the muscarinic acetylcholine receptor (mAChR) blocker atropine (Atr), or classic α7 nicotine acetylcholine receptor (α7nAChR) antagonist methyllycaconitine (MLA) 1 hour before administration of AChEIs-donepezil (4 mg/kg), rivastigmine (2 mg/kg), huperzine A (0.2 mg/kg), or neostigmine (0.15 mg/kg)-followed by APAP (300 mg/kg). Eight hours later, the mice were euthanized for histopathologic examination and biochemical assay. The results demonstrated that the tested AChEIs, excluding neostigmine, could attenuate APAP-induced liver injury, accompanied by reduced reactive oxygen species formation, adenosine triphosphate and cytochrome C loss, c-Jun N-terminal kinase 2 (JNK2) phosphorylation, and cytokines. However, Atr or MLA significantly weakened the protective effect of AChEI by affecting mitochondrial function or JNK2 phosphorylation and inflammation response. These results suggest that central mAChR and α7nAChR, which are activated by accumulated acetylcholine resulting from AChEI, were responsible for the protective effect of AChEIs on APAP-induced liver injury. This indicates that Alzheimer's patients treated with AChEI could take APAP, as AChEI is unlikely to deteriorate the hepatotoxicity of APAP.

The HSD2 (11-beta-hydroxysteroid dehydrogenase-type 2 enzyme) containing neurons of the nucleus tractus solitarius (NTS) become activated during low-sodium and high-aldosterone states such as hypovolemia. This response may be due to hormonal and/or neural signals. Hormonal signals may activate neurons in the area postrema that innervate the HSD2 neurons. The vagus nerve projects directly to the HSD2 neurons and this could be another route whereby these neurons receive information about systemic sodium/aldosterone status. The peripheral sites of origin that contribute to this vagal projection remain unknown, and in the present study, we injected the transganglionic tracer, cholera toxin beta-subunit-horseradish peroxidase (CTb-HRP), into wall of various gastrointestinal organs (stomach, small and large intestine) or liver of rats. Confocal microscopy of brainstem sections stained by a double immunohistochemical procedure was used to analyze whether the HSD2 neurons received axonal contacts from specific gastrointestinal structures. The major source of afferents arose from the stomach, mainly from its pyloric antrum, but a weaker input originated from the fundus region. A trace amount originated from the duodenum. The terminal part of the small intestine and large intestine did not to contribute to this projection. Similarly, no afferent inputs from the liver or portal vein were found. In conclusion, HSD2 neurons receive an input mainly from the stomach and these results are considered as potential sites affecting sodium intake.

The purpose of this study was to investigate the physiologic changes of ketone bodies in patients with aneurysmal subarachnoid hemorrhage. We tested the hypothesis that the plasma ketone bodies are associated with the vasoconstrictor and lipolysis effect of circulating catecholamine.

Twenty-four patients with mild aneurysmal subarachnoid hemorrhage and 18 healthy volunteers were enrolled in this study. We collected arterial blood samples immediately after admission and 30 days later to measure the levels of 3-hydroxybutyrate, acetoacetate, epinephrine and norepinephrine.

At the onset of aneurysmal subarachnoid hemorrhage, the plasma ketone body (3-hydroxybutyrate + acetoacetate) level and the epinephrine and norepinephrine concentrations were significantly elevated, but the arterial ketone body ratio (acetoacetate/3-hydroxybutyrate) was significantly decreased compared with that of the control group. There was a negative correlation between the plasma ketone body level and the arterial ketone body ratio. There was a positive correlation between the plasma ketone body level and epinephrine level. Thirty days after admission, the ketone body, epinephrine and norepinephrine levels, as well as the arterial ketone body ratio, showed no significant differences between the patients and controls.

At the onset of mild aneurysmal subarachnoid hemorrhage, the plasma ketone body level was significantly increased, while the arterial ketone body ratio was significantly decreased.

Various factors involved in the development of liver fibrosis, including hepatic stellate cells (HSCs), cholinergic nervous activity and fibrogenetic cytokines. The present study aims to investigate the role of cholinergic regulation in the promoting of liver fibrogenesis relating to bone morphogenetic protein-6 (BMP-6) and/or transforming growth factor-beta1 (TGFbeta1). We treated carbon tetrachloride (CCl(4)) into rats for eight weeks to induce liver fibrosis and arranged these rats for cholinergic denervation, hepatic branch vagotomy or atropine administration. Acetylcholinesterase (AChE) staining showed the distribution of cholinergic nerve around fibrosis scaring septa. The immunohistochemical staining for alpha smooth muscle actin (alphaSMA) indicated the less HSCs in CCl(4) treated rat liver with cholinergic denervation as compared to the sham-operated CCl(4) treated rats. It seems that cholinergic nerve not only innervates around the fibrosis area but also promotes HSCs. We also detected TGFbeta1 and BMP-6 expressions using RT-PCR and immunohistochemistry. The obtained results show that cholinergic denerveration decreases BMP-6 and TGF-beta1 expressions in CCl(4) induced liver fibrosis of rats. In conclusion, cholinergic nerve may influence HSCs in addition to the lowering of BMP-6 and TGF-beta1 gene expressions to modify liver fibrosis.

Constancy of hepatic blood flow (HBF) is crucial for several homeostatic roles. The present conceptual review focuses on interrelated mechanisms that act to maintain a constant HBF per liver mass. The liver cannot directly control portal blood flow (PF); therefore, these mechanisms largely operate to compensate for PF changes. A reduction in PF leads to reduced intrahepatic distending pressure, resulting in the highly compliant hepatic vasculature passively expelling up to 50% of its blood volume, thus adding to venous return, cardiac output and HBF. Also activated immediately upon reduction of PF are the hepatic arterial buffer response and an HBF-dependent hepatorenal reflex. Adenosine is secreted at a constant rate into the small fluid space of Mall which surrounds the terminal branches of the hepatic arterioles, portal venules and sensory nerves. The concentration of adenosine is regulated by washout into the portal venules. Reduced PFreduces the washout and the accumulated adenosine causes dilation of the hepatic artery, thus buffering the PF change. Adenosine also activates hepatic sensory nerves to cause reflex renal fluid retention, thus increasing circulating blood volume and maintaining cardiac output and PF. If these mechanisms are not able to maintain total HBF, the hemodynamic imbalance results in hepatocyte proliferation, or apoptosis, by a shear stress/nitric oxide-dependent mechanism, to adjust total liver mass to match the blood supply. These mechanisms are specific to this unique vascular bed and provide an excellent example of multiple integrative regulation of a major homeostatic organ.

The liver function and perfusion following brain death is mainly influenced by the sympathetic nerves and hormones. We examined the specific influence of surgical liver denervation on systemic and hepatic perfusion parameters, bowel ischemia and oxidative stress in hemodynamically stable BD and control (living donor [LD]) pigs. Brain death was induced in 8 pigs via saline infusion into the balloon of an epidural Tieman-catheter (1 mL/15 minutes) and compared to the control group (n = 6) over 4 hours. At 2 hours postoperatively, complete liver denervation was initiated. We analyzed systemic cardiocirculatory parameters (mean arterial pressure, aortic flow, bowel ischemia (endotoxin, and endotoxin-neutralizing capacity) and oxidative stress (total glutathione in erythrocytes [tGSH(E)]) and compared them to local/hepatic perfusion parameters (hepatic artery and portal venous flow, liver blood flow index, and microperfusion), local bowel ischemia (intramucosal pH [pHi] of stomach [pHi(S)]/colon[pHi(C)]), and liver oxidative stress (glutathione [rGSH(L), GSSG(L)]). Following brain death, the parameters including mean arterial pressure, aortic flow, pHi, endotoxin, and tGSH(E) showed no significant changes at 2 hours. Portal venous flow and microperfusion were decreased significantly and hepatic arterial buffer response was ineffective. Hepatic oxidative stress was increased in BD animals (decrease rGSH(L), increase GSSG(L)). Surgical denervation/manipulation increased portal venous flow significantly, hepatic arterial buffer response became effective, and stomach pHi decreased (BD and LD groups). Hepatic oxidative stress was reduced in the BD group (increase rGSH(L)/GSSG(L); P < 0.001) while it was increased in the LD group (decrease rGSH(L)/GSSG(L); P < 0.001). In conclusion, denervation reduces hepatic oxidative stress in BD only in contrast to the LD. The reciprocal effect of denervation depends on the state of neural activation and postulates a potential benefit of surgical denervation before organ harvesting in brain death.

We have demonstrated changes in the circadian rhythm of plasma protein C levels in patients with autonomic dysfunction and liver-transplanted patients, compared with that in healthy volunteers. The circadian rhythm of protein C serves as a useful marker to screen for autonomic dysfunction in the liver.

Vagal and spinal afferent innervation of the portal hepatic area has not been studied as thoroughly as the innervation of other important organs. It is generally agreed that unlike noradrenergic sympathetic efferent nerve fibers, sensory nerve fibers of either vagal or dorsal root/spinal origin do not directly innervate hepatocytes, but are restricted to the stroma surrounding triades of hepatic vasculature and bile ducts, and to extrahepatic portions of the portal vein and bile ducts. For vagal afferent innervation, retrograde and anterograde tracing studies in the rat have clearly shown that only a minor portion of the common hepatic branch innervates the liver area, while the major portion descends in the gastroduodenal branch toward duodenum, pancreas, and pylorus. Hepatic paraganglia, bile ducts, and portal vein receive the densest vagal afferent innervation. Calretinin may be a relatively specific marker for vagal afferent innervation of the portal-hepatic space. Calcitonin gene-related peptide (CGRP) is a specific marker for dorsal root afferents, and CGRP-immunoreactive fibers are mainly present near the intrahepatic vascular bundles and bile ducts, and in the same extrahepatic compartments that contain vagal afferents. Because of the specific anatomical organization of hepatic nerves, selective hepatic denervation, whether selective for the vagal or sympathetic division, or for efferents and afferents, is nearly impossible. Great caution is therefore necessary when interpreting functional outcomes of so-called specific hepatic denervation studies.

Central administration of thyrotropin-releasing hormone (TRH) enhances hepatic blood flow in animal models. TRH nerve fibers and receptors are localized in the dorsal vagal complex (DVC), and retrograde tracing techniques have shown that hepatic vagal nerves arise mainly from the left DVC. However, nothing is known about the central sites of action for TRH to elicit the stimulation of hepatic blood flow. The effect of microinjection of a TRH analogue into the DVC on hepatic blood flow was investigated in urethane-anesthetized rats. After measuring basal flow, a stable TRH analogue (RX-77368) was microinjected into the DVC and hepatic blood flow response was observed for 120 minutes by laser Doppler flowmetry. Either left or right cervical vagotomy or hepatic branch vagotomy was performed 2 hours before the peptide. Microinjection of RX-77368 (0.5-5 ng) into the left DVC dose-dependently increased hepatic blood flow. The stimulation of hepatic blood flow by RX-77368 microinjection into the left DVC was eliminated by left cervical and hepatic branch vagotomy but not by right cervical vagotomy. By contrast, microinjection of RX-77368 into the right DVC did not significantly alter hepatic blood flow. These results suggest that TRH acts in the left DVC to stimulate hepatic blood flow through the left cervical and hepatic vagus, indicating that neuropeptides may act in the specific brain nuclei to regulate hepatic function.

Infusion of glucose into the hepatic artery blocks the stimulatory effect of the "portal signal" on net hepatic glucose uptake (NHGU) during portal glucose delivery. We hypothesized that hepatic artery ligation (HAL) would result in enhanced NHGU during peripheral glucose infusion because the arterial glucose concentration would be perceived as lower than that in the portal vein. Fourteen dogs underwent HAL approximately 16 days before study. Conscious 42-h-fasted dogs received somatostatin, intraportal insulin, and glucagon infusions at fourfold basal and at basal rates, respectively, and peripheral glucose infusion to create hyperglycemia. After 90 min (period 1), seven dogs (HALpo) received intraportal glucose (3.8 mg. kg-1. min-1) and seven (HALpe) continued to receive only peripheral glucose for 90 min (period 2). These two groups were compared with nine non-HAL control dogs (control) treated as were HALpe. During period 2, the arterial plasma insulin concentrations (24 +/- 3, 20 +/- 1, and 24 +/- 2 microU/ml) and hepatic glucose loads (39.1 +/- 2.5, 43.8 +/- 2.9, and 37.7 +/- 3.7 mg. kg-1. min-1) were not different in HALpe, HALpo, and control, respectively. HALpo exhibited greater (P < 0.05) NHGU than HALpe and control (3.1 +/- 0.3, 2.0 +/- 0.4, and 2.0 +/- 0.1 mg. kg-1. min-1, respectively). Net hepatic carbon retention was approximately twofold greater (P < 0.05) in HALpo than in HALpe and control. NHGU and net hepatic glycogen synthesis during peripheral glucose infusion were not enhanced by HAL. Even though there exists an intrahepatic arterial reference site for the portal vein glucose concentration, the failure of HAL to result in enhanced NHGU during peripheral glucose infusion suggests the existence of one or more comparison sites outside the liver.

The aim of the present study was to investigate how hepatic blood flow (HBF) changes in response to mechanical stimulation of different areas of the skin in anaesthetised rats, by focusing on involvement of the hepatic sympathetic nerves in and contribution of systemic circulatory changes to the HBF responses. HBF was measured at the surface of the left lateral lobe using the laser Doppler flowmetry. Both innocuous and noxious mechanical stimuli were applied to skin areas of the abdomen and hindlimb. Innocuous mechanical stimulation (brushing) of the abdomen and hindlimb did not significantly change HBF, while noxious mechanical stimulation (pinching) of the abdomen and hindlimb did. The responses to pinching were dependent on the sites stimulated. Pinching of the abdomen decreased, while pinching of the hindlimb increased the HBF. The decrease of HBF in response to abdominal pinching remained after the spinal cord was transected at T1-2 level, but the response was diminished after hepatic sympathetic nerves were severed. On the other hand, the increase of HBF in response to hindlimb pinching was dependent on the increase in blood pressure, and was not influenced by the severance of hepatic sympathetic nerves, and the responses to hindlimb pinching were almost absent after the spinal cord was transected. Based on these results, we suggest that noxious mechanical stimulation of the skin produces changes of HBF, either as a reflex response via activation of the hepatic sympathetic nerves or as a passive response to systemic circulatory changes, depending on the sites stimulated.

The aim of the present study was to elucidate the influence of the hepatic sympathetic and parasympathetic (vagal) nerves on the hepatic blood flow (HBF), both tonically and when stimulated, using urethane-anesthetized rats as an in vivo experimental model. HBF was measured at the surface of the lateral left lobe of the liver using laser Doppler flowmetry and the hydrogen gas clearance method. Denervation of the hepatic sympathetic nerves had no influence on the HBF, while electrical stimulation of the hepatic sympathetic nerves caused the HBF to decrease in a frequency-dependent manner. This decrease was shown to occur via alpha-adrenergic receptors. In contrast, neither denervation nor electrical stimulation of the hepatic vagal nerves elicited significant changes in the HBF. These results demonstrate that the sympathetic and vagal hepatic nerves have little or no tonic influence on the HBF of rats under urethane anesthesia, whereas the HBF decreases in response to activation of the hepatic sympathetic nerves.

. The effects of dopamine (DA) on systemic hemodynamics are better understood than its effects on hepatic hemodynamics, especially after liver denervation occurring during liver transplantation. Therefore, a porcine model was used to study DA's effects on hemodynamics after hepatic denervation.

Fifteen pigs underwent laparotomy for catheter and flow probe placement. The experimental group (n = 7) also underwent hepatic denervation. After 1 week, all pigs underwent DA infusion at increasing doses (3-30 mcg/kg/min) while measuring hepatic parameters [portal vein flow (PVF), hepatic artery flow (HAF), total hepatic blood flow (THBF = HAF + PVF), portal and hepatic vein pressures] and systemic parameters [heart rate (HR), mean arterial pressure (MAP)].

There was a significant increase in HAF from baseline to the 30 mcg/kg/min DA infusion rate (within-subjects P < 0.01), but the differences between the two groups were not significant. PVF and THBF showed large effects (increases) with denervation, but the increase in flow with DA infusion was not present after denervation. Perihepatic pressures were unchanged by denervation or DA. Heart rate differed significantly between the control and denervated animals at baseline, 3, 6, 12 (all P < 0.05), and 30 mcg/kg/min DA (P = 0.10). Control vs denervation MAP at baseline was 100 +/- 4 vs 98 +/- 4 Torr and at 30 mcg/kg/min it was 110 +/- 3 vs 101 +/- 5 mm Hg.

Hepatic flows tended to be higher after denervation. HAF showed similar increases with DA in both control and denervation groups. Increases in PVF and THBF with DA infusion were not present after denervation. HR was significantly decreased and MAP tended to be lower after denervation. The HR and MAP response to DA was similar in both groups. Therefore, both denervation and DA infusion have an effect on systemic and hepatic hemodynamics.

Our laboratory has previously demonstrated that hypoglycemic detection occurs in the portal vein, not the liver. To ascertain whether hypoglycemic detection may also occur in the hepatic artery, normoglycemia was established across the liver via a localized hepatic artery glucose infusion. Male mongrel dogs (n = 7) were infused with insulin (5.0 mU x kg(-1) x min(-1)) via the jugular vein to induce systemic hypoglycemia. Animals participated in two hyperinsulinemic-hypoglycemic clamp experiments distinguished by the site of glucose infusion. During the liver irrigation protocol, glucose was infused via the hepatic artery (HA protocol) to maintain liver normoglycemia as systemic glucose concentrations were systematically lowered over 260 min (nadir = 2.2 +/- 0.01 mmol/l). During control experiments, glucose was infused peripherally (PER protocol) to control reductions in blood glucose. Arterial glucose concentrations were not significantly different at any time between the two protocols (P = 0.73). Hepatic artery and liver glucose concentrations were significantly elevated in the HA versus PER protocol throughout the duration of the progressive hyperinsulinemic-hypoglycemic clamp. During the PER protocol, epinephrine and norepinephrine concentrations increased significantly above basal values (0.53 +/- 0.06 and 0.85 +/- 0.2 nmol/l, respectively) to plateaus of 4.4 +/- 0.86 (P = 0.0001) and 3.6 +/- 0.69 nmol/l (P = 0.001), respectively. There were no significant differences between the two protocols in the epinephrine (P = 0.81) and the norepinephrine (P = 0.68) response to hypoglycemia. The current findings indicate that glucosensors important to hypoglycemic detection do not reside in the hepatic artery. Furthermore, these data confirm our previous findings that glucosensors important to hypoglycemic detection are not present in the liver, but are in fact localized to the portal vein.

Hepatic arteries are reportedly innervated by vasoconstrictor and vasodilator nerves. Experiments were carried out to investigate the possible involvement of calcitonin gene related peptide (CGRP) and nitric oxide as neurotransmitters during the relaxation of the rat common hepatic artery produced by transmural electrical field stimulation (ES). Common hepatic arteries were excised under ether-anesthesia from 6 weeks-old female rats, and isometric tensions recorded from endothelium-damaged ring preparations. In the presence of atropine and guanethidine, ES relaxed arteries which had been previously contracted with vasopressin. The relaxation response to ES was attenuated by either tetrodotoxin or capsaicin-pretreatment. CGRP induced a concentration-dependent relaxation, which was inhibited by the CGRP antagonist CGRP(8-37). The ES-induced relaxation was attenuated either slightly by the nitric oxide synthesis inhibitor L-nitroarginine (L-NNA) or markedly by CGRP(8-37). The relaxation response was nearly abolished in the presence of both CGRP(8-37) and L-NNA. These results may indicate that the nerve stimulation-induced vasodilatation of the rat common hepatic artery is mediated mainly by CGRP and partly by nitric oxide.

The Fischer 344 rat was found to be extremely sensitive to the diabetogenic effects of neonatally injected streptozotocin (STZ): injection of 40-100 mg/kg STZ at 1.5 days postnatal produced in the adult graded levels of hyperglycemia in males but not the females. The optimal dose in the 1.5 day old male was 80 mg/kg: it produced hyperglycemia without affecting growth or thyroid status in the adult. The neonatally STZ-injected adult rat displayed characteristics consistent with type II diabetes: mild hyperglycemia accentuated by fasting or consumption of a high fat diet; little change in insulin levels; slight elevation in glucagon levels; no alterations in ketones. Using radioligand binding techniques to isolated rat liver plasma membranes, compared to the control state, the type II diabetic state was found to have: no effect on either alpha(2)- or beta-adrenergic receptor binding; a decrease in the major dominant alpha(1)-adrenergic receptor, reflecting a decrease in receptor numbers but not their affinity; an increase in the plasma membrane calcium transport system, potentially depleting intracellular calcium stores essential for producing an alpha(1)-adrenergic receptor response. Since the alpha(1)-adrenergic receptor-calcium effector system is critical for the actions of catecholamines in the rat, these results suggest that the liver in the type II diabetic state may be refractory to the actions of catecholamines. We propose that the diabetes-evoked decrease in the dominant adrenergic receptor-effector system through which catecholamines act may be the cellular expression of defective glucocounterregulation in the diabetic state.

Studies were performed on the effects of activation of afferent nerves with capsaicin (5 mg/kg i.p.) and lesioning of these nerves with neurotoxic doses of capsaicin (50 mg/kg, s.c. in two-day-old rats and 200 mg/kg s.c. in adult rats) on serum glucose and free fatty acid (FFA) concentrations in conditions of changing glucose levels induced by administration of insulin and glucose to starved (16 h) Wistar rats. These studies showed that capsaicin stimulation of intact rats decreased the hypoglycemic action of insulin, increased hyperglycemia following glucose dosage, increased FFA levels, and prevented the FFA-lowering effect of insulin. Neonatal treatment with capsaicin decreased the hypoglycemic effect of insulin but had no effect on hyperglycemia following glucose doses, but decreased FFA levels. Treatment of adult rats with neurotoxic doses of capsaicin did not alter the effect of insulin on glucose levels and decreased FFA concentrations. Capsaicin stimulation in rats following treatment with neurotoxic doses had no effect on the hypoglycemic action of insulin, but prevented it from affecting the FFA concentration.

Intestinal glucose uptake (GUi) from blood increased when blood flow (BF) was increased. The increase in BF could elevate shear stress. Therefore, we hypothesize that shear stress-induced release of autacoids mediates the increase in GU(i). A surgically separated segment of small intestine was perfused in situ with the use of an arterial circuit in anesthetized cats. Arterial and portal blood samples were taken simultaneously for assessment of GU(i). Adenosine was used to elevate intestinal BF. The GU(i) increased by 45.0 +/- 18.3 from 25.3 +/- 3.8 micromol. min(-1). 100 g tissue(-1) when the BF increased about four times. It was not a direct effect of adenosine because GU(i) was not altered if the flow was held constant. This increase was blocked by a cyclooxygenase inhibitor, indomethacin, but not by nitric oxide synthase blocker N(G)-nitro-L-arginine methyl ester. Furthermore, prostaglandin F(2alpha) (PGF(2alpha)) but not PGE(2) or PGI(2) reversed the blockade of the increase in GU(i) after indomethacin during elevated blood flow, whereas they had no influence on basal uptake. The results suggest that shear stress-induced release of PGF(2alpha) mediated the increase in GU(i) when blood flow was elevated.

Peripheral osmoreceptors monitor dietary NaCl and modify central nervous system and renal sympathetic nervous system activity accordingly. Experimental evidence suggests that these responses are dependent on the hepatic nerves. Peripheral osmoreceptors also modify arginine vasopressin (AVP) secretion. However, although hepatic denervation reportedly blunts activation of both supraoptic and paraventricular hypothalamic neurons after intraportal NaCl infusion, the role of the hepatic nerves in the AVP release has not been directly examined. The present study tests the hypothesis that the hepatic nerves modify AVP release in response to intragastric NaCl infusion. Wistar-Kyoto rats (WKY) received either hepatic denervation or a sham operation. Intragastric NaCl infusion significantly elevated plasma AVP in both sham-operated WKY and hepatic-denervated WKY, and the responses were not different between these groups. Second, previous studies suggest that both AVP secretion and baroreflexes are blunted in spontaneously hypertensive rats (SHR), deficits that contribute to the observed hypertension in SHR. We hypothesized that SHR also have a blunted peripheral osmoreceptor reflex and that this contributes to NaCl-sensitive hypertension. In contrast to our prediction, in SHR intragastric NaCl infusion induced an increase in plasma AVP that was similar to that in the WKY groups. Thus, although hepatic osmoreceptors are important for chronic regulation of arterial pressure, renal sympathetic nervous system activity, and the activity of hypothalamic neurons, they do not appear to influence plasma AVP concentration in response to intragastric NaCl.

1. This study examined the extent of liver perfusion and its oxygenation during progressive haemorrhage. We examined hepatic arterial flow and hepatic oxygenation following the reduced portal flow during haemorrhage in 18 pigs. The hepatic surface oxygenation was assessed by near-infrared spectroscopy and the hepatic metabolism of oxygen, lactate and catecholamines determined the adequacy of the hepatic flow. 2. Stepwise haemorrhage until circulatory collapse resulted in proportional reductions in cardiac output and in arterial, central venous and pulmonary wedge pressures. While heart rate increased, pulmonary arterial pressure remained stable. In addition, renal blood flow decreased, renal vascular resistance increased and there was elevated noradrenaline spill-over. Further, renal surface oxygenation was lowered from the onset of haemorrhage. 3. Similarly, the portal blood flow was reduced in response to haemorrhage, and, as for the renal flow, the reduced splanchnic blood flow was associated with an elevated noradrenaline spill-over. In contrast, hepatic arterial blood flow was only slightly reduced by haemorrhage, and surface oxygenation did not change. The hepatic oxygen uptake was maintained until the blood loss represented more than 30 % of the estimated blood volume. At 30 % reduced blood volume, hepatic catecholamine uptake was reduced, and the lactate uptake approached zero. 4. Subsequent reduction of cardiac output and portal blood flow elicited a selective dilatation of the hepatic arterial vascular bed. Due to this dilatation liver blood flow and hepatic cell oxygenation and metabolism were preserved prior to circulatory collapse.

Central neuropeptides play a role in many physiological regulatory processes through the autonomic nervous system. Thyrotropin-releasing hormone (TRH) is distributed in the central nervous system and acts as a neurotransmitter to regulate gastric functions through vagal-muscarinic pathways. The central effect of the TRH analog on hepatic blood flow was investigated in urethan-anesthetized rats. Hepatic blood flow was determined by the hydrogen gas clearance technique. Intracisternal injection of the stable TRH analog RX-77368 (5-100 ng) dose dependently increased hepatic blood flow with peak response at 15 min after the peptide was administered (net change from basal for vehicle and 5, 10, 100, and 500 ng RX-77368 was 2.0 +/- 0.2, 8.9 +/- 0.8, 19.4 +/- 2.6, 32.6 +/- 3.3, and 28.5 +/- 6.8 ml.min-1.100 g-1, respectively), and this stimulatory effect returned to baseline at 90 min. The stimulation of hepatic blood flow by the intracisternally administered TRH analog was abolished by atropine methyl nitrate (0.15 mg/kg ip), indomethacin (5 mg/kg ip), NG-nitro-L-arginine methyl ester (10 mg/kg iv), and hepatic branch vagotomy but not by cervical spinal cord transection (C6 level). Intravenous injection of RX-77368 did not have any effect on hepatic blood flow. These results indicate that TRH acts in the central nervous system to stimulate hepatic blood flow through vagal-muscarinic and indomethacin- and nitric oxide-dependent pathways.

Our aim was to determine whether vagal transmission is required for the hormonal response to insulin-induced hypoglycemia in 18-h-fasted conscious dogs. Hollow coils were placed around the vagus nerves, with animals under general anesthesia, 2 wk before an experiment. On the day of the study they were perfused with -15 degrees C ethanol for the purpose of blocking vagal transmission, either coincident with the onset of insulin-induced hypoglycemia or after 2 h of established hypoglycemia. In a separate study the coils were perfused with 37 degrees C ethanol in a sham cooling experiment. The following parameters were measured: heart rate, arterial plasma glucose, insulin, pancreatic polypeptide, glucagon, cortisol, epinephrine, norepinephrine, glycerol, free fatty acids, and endogenous glucose production. In response to insulin-induced hypoglycemia (42 mg/dl), plasma glucagon peaked at a level that was double the basal level, and plasma cortisol levels quadrupled. Plasma epinephrine and norepinephrine levels both rose considerably to 2,135 +/- 314 and 537 +/- 122 pg/ml, respectively, as did plasma glycerol (330 +/- 60%) and endogenous glucose production (150 +/- 20%). Plasma free fatty acids peaked at 150 +/- 20% and then returned to basal levels by the end of the study. The hypoglycemia-induced changes were not different when vagal cooling was initiated after the prior establishment of hypoglycemia. Similarly, when vagal cooling occurred concurrently with the initiation of insulin-induced hypoglycemia (46 mg/dl), there were no significant differences in any of the parameters measured compared with the control. Thus vagal blockade did not prevent the effect on either the hormonal or metabolic responses to low blood sugar. Functioning vagal afferent nerves are not required for a normal response to insulin-induced hypoglycemia.

Hepatic neuropeptide Y (NPY) innervation was studied by immunohistochemistry in various mature vertebrates including the eel, carp, bullfrog, turtle, chicken, mouse, rat, guinea pig, dog, monkey, and human. In addition, an ontogenetic study on hepatic NPY was made in developing mice and guinea pigs. In all species examined except the eel, NPY-like immunoreactivity was detected in nerve fibers. In the carp, bullfrog, turtle, chicken, mouse, and rat, NPY-positive fibers were distributed around the wall of hepatic vessels and the bile duct of the Glisson's sheath. The density of NPY-positive fibers increased with evolution. However, in the guinea pig, dog, monkey, and human, numerous NPY-positive fibers were observed not only in the Glisson's sheath but also in the liver parenchyma. Positive fibers formed a dense network that surrounded the hepatocytes. The present immunoelectron microscopic study has confirmed that NPY-positive terminals are closely apposed to hepatocytes. Ontogenically, NPY-positive fibers were first found in the embryonic liver of 19-day-old mice. Positive fibers increased with age, and the highest peak was seen 1 week after birth. However, NPY-positive nerve fibers were present abundantly in Glisson's sheath and in the hepatic parenchyma of neonatal (3 and 7 days old) guinea pigs in a distribution similar to that in mature animals. This ontogenetic pattern suggests that NPY plays a certain role in the developing liver.

This study was undertaken to examine the effects of the activation of the neurons in the nucleus tractus solitarius (NTS) via microinjection of sodium nitroprusside (SNP), which spontaneously releases nitric oxide (NO), on the blood flows of the spleen, kidney, liver, brain and spinal cord and to investigate the regional differentiation of the blood flow changes between those organs. Employing urethane-anesthetized (1.5 g kg-1, i.p.), paralyzed and artificially ventilated rats, regional blood flows of those organs were determined simultaneously using radiolabeled microspheres (109Cd, 51Cr and 85Sr) Unilateral microinjection of SNP into the NTS (n = 9) decreased brain blood flow from 71 +/- 8 (mean +/- S.E.) to 54 +/- 6 (P < 0.01) and spinal cord blood flow from 58 +/- 8 to 43 +/- 5 ml min-1 (100 g)-1 (P < 0.05) and increased brain vascular resistance from 1.18 +/- 0.13 to 1.48 +/- 0.15 (P < 0.01) and spinal cord vascular resistance from 1.46 +/- 0.17 to 1.80 +/- 0.16 (P < 0.05) mmHg per [ml min-1 (100 g)-1]. Whereas the microinjection of SNP into the NTS increased splenic blood flow from 127 +/- 25 to 188 +/- 27 (P < 0.01) and renal blood flow from 346 +/- 28 to 371 +/- 26 ml min-1 (100 g) (P < 0.05) and decreased splenic vascular resistance from 0.77 +/- 0.13 to 0.44 +/- 0.06 (P < 0.01) and renal vascular resistance from 0.24 +/- 0.02 to 0.21 +/- 0.01 mmHg per [ml min-1 (100 g)-1] (P < 0.05). The blood flow of the liver was not significantly altered. Unilateral microinjection of NG-monomethyl-L-arginine, an inhibitor of the formation of NO from L-arginine, into the NTS (n = 10) did not significantly change the blood flows of all organs examined except for an increase in blood flow of the kidney. Unilateral microinjections of SNP into the area adjacent to the NTS (n = 9), of artificial cerebrospinal fluid into the NTS (n = 7) and of light-inactivated SNP into the NTS (n = 6) did not significantly alter the blood flows of all organs examined. These results suggest than the neurons in the NTS have a vasoconstrictor effect on the brain and spinal cord circulation and a vasodilator effect on the splenic and renal circulation. There is a regional qualitative differentiation of the blood flow responses between these organs during activation of the neurons in the NTS.

Our goal was to determine whether basal sympathetic tone to the kidney and various peripheral tissues is altered in conscious diabetic rats. Norepinephrine (NE) turnover was determined by measuring the decline in tissue NE concentration ([NE]) at 4 and 8 h after administering alpha-methyl-p-tyrosine to animals from each of three groups, diabetic (STZ injected 4 weeks prior to experimentation), diabetic + insulin (STZ injected; insulin injected; 2 U/day per rat for 4 weeks) and control (n = 18-20 per group). Various peripheral tissues (duodenum, left ventricle of the heart, kidney, skeletal muscle, left adrenal gland and liver) were examined. [NE] was significantly increased in the kidney and liver, but decreased in the duodenum of the diabetic compared to the control rats. In contrast to the changes in [NE], the rate constant, which provides an index of sympathetic tone, increased in the duodenum and liver, and a decreased in the adrenal gland. The turnover of NE, which is a composite of [NE] and rate constant, increased in the kidney and liver, and decreased in the adrenal gland of diabetic rats. Chronic treatment of diabetic rats with insulin normalized NE turnover in the liver, but not in the adrenal gland. Diabetic rats treated with insulin exhibited a reduced turnover of NE in the kidneys. These data demonstrate that there are differential changes in the [NE], rate constant, and turnover of NE in diabetic rats. Overall, these data indicate that there is increased noradrenergic activity to the kidney, possibly related to sodium retention, and a differential change in noradrenergic activation to various peripheral tissues in diabetic rats.

The ventromedial hypothalamic nucleus (VMH) is necessary for the integrated hormonal response to hypoglycemia. To determine the role of the VMH as a glucose sensor, we performed experiments designed to specifically prevent glucopenia in the VMH, while producing hypoglycemia elsewhere. We used awake chronically catheterized rats, in which local VMH glucose perfusion (100 mM or 15 mM of D-glucose) was combined with a sequential euglycemic-hypoglycemic clamp. In two control groups the VMH was perfused either with (a) an iso-osmotic solution lacking glucose, or with (b) nonmetabolizable L-glucose (100 mM). During systemic hypoglycemia glucagon and catecholamine concentrations promptly increased in the control animals perfused with either 100 mM L-glucose or the iso-osmotic solution lacking glucose. In contrast, glucagon, epinephrine and norepinephrine release was inhibited in the animals in which the VMH was perfused with D-glucose; hormonal secretion was partially suppressed by the VMH perfusion with 15 mM D-glucose and suppressed by approximately 85% when the VMH was perfused with 100 mM D-glucose, as compared with the control groups. We conclude that the VMH must sense hypoglycemia for full activation of catecholamine and glucagon secretion and that it is a key glucose sensor for hypoglycemic counterregulation.

The recent recognition that insulin resistance is associated with a number of risk factors for atherosclerotic cardiovascular disease has increased the interest in agents that are able to improve insulin sensitivity. The capacity of benfluorex (Médiator) to enhance insulin action has led to much speculation regarding its mechanism of action. Chronic benfluorex treatment, in a variety of genetic and dietary animal models of diabetes and insulin resistance, has been shown to diminish, circulating insulin levels and to decrease blood glucose, triglycerides, and cholesterol concentrations. From these studies, it is possible to postulate a multifactorial mode of action of this drug that involves three independent but interactive processes: (1) a direct effect on insulin target tissues, mediated by mechanisms distal to the binding of insulin to its receptor, (2) modulation of the glucoregulatory hormone balance, including a diminution in both adrenal and sympathetic tone, leading to improved hepatic sensitivity to insulin, and (3) reduced hepatic and muscle lipid availability, leading to improved glucose utilization in skeletal muscle. The multiplicity of the neuroendocrine and biochemical effects of benfluorex cannot be explained by a single cellular or molecular action. It has been suggested that insulin sensitizers may act on key molecules involved in the sequence of biochemical events involving the insulin signal transduction process. The identification of these molecular targets and the determination of their relative importance in the treatment of type II diabetes remains to be established and constitutes the main subject of ongoing research with benfluorex.

The study aim was to investigate the role of the parasympathetic nervous system in the control of glucose tolerance in man. Glucose kinetics were determined during an oral glucose tolerance test (OGTT) in six subjects with truncal vagotomies and six control subjects. Basal plasma glucose levels in the two groups were equal; however, 20 to 40 minutes after the OGTT, glucose was higher in vagotomized compared with control subjects (P < .02). There were no differences in insulin levels between the subjects. Glucagon decreased after the OGTT in the controls, whereas in the vagotomized subjects it increased transiently and did not decrease beyond basal levels. There was no difference in basal hepatic glucose production, but suppression was greater in controls in the first 10 minutes (P < .01). Gut-derived glucose appearance increased faster and to a higher level (56.0 +/- 8 v 29.7 +/- 2.9 mumol/kg/min, P < .02) in vagotomized subjects. There were no differences in the metabolic clearance rate of glucose between the two groups. It is concluded that parasympathetic innervation of the pancreas is essential for suppression of glucagon secretion during hyperglycemia. However, abnormal glucose tolerance in vagotomized subjects is primarily due to rapid gut glucose absorption, with the denervated parasympathetic system playing only a minor role.

We assessed the combined role of epinephrine and glucagon in regulating gluconeogenic precursor metabolism during insulin-induced hypoglycemia in the overnight-fasted, adrenalectomized, conscious dog. In paired studies (n = 5), insulin was infused intraportally at 5 mU.kg-1.min-1 for 3 h. Epinephrine was infused at a basal rate (B-EPI) or variable rate to simulate the normal epinephrine response to hypoglycemia (H-EPI), whereas in both groups the hypoglycemia-induced rise in cortisol was simulated by cortisol infusion. Plasma glucose fell to approximately 42 mg/dl in both groups. Glucagon failed to rise in B-EPI, but increased normally in H-EPI. Hepatic glucose release fell in B-EPI but increased in H-EPI. In B-EPI, the normal rise in lactate levels and net hepatic lactate uptake was prevented. Alanine and glycerol metabolism were similar in both groups. Since glucagon plays little role in regulating gluconeogenic precursor metabolism during 3 h of insulin-induced hypoglycemia, epinephrine must be responsible for increasing lactate release from muscle, but is minimally involved in the lipolytic response. In conclusion, a normal rise in epinephrine appears to be required to elicit an increase in glucagon during insulin-induced hypoglycemia in the dog. During insulin-induced hypoglycemia, epinephrine plays a major role in maintaining an elevated rate of glucose production, probably via muscle lactate release and hepatic lactate uptake.

Total parenteral nutrition (TPN) is essential for maintaining the nutritional status of patients who are unable to eat sufficiently to meet their metabolic needs. However, TPN suppresses appetite and ultimately diminishes food intake. Theories concerning the role(s) of peripheral metabolites as signals, acting via the liver and the hypothalamus, for the metabolic control of food intake, have been put forward to explain the anorectic effect of TPN. In addition, it is postulated that changes in peripheral metabolites during TPN may be translated into changes in the levels of brain neurotransmitters known to decrease food intake. This review summarizes studies concerning the effect of TPN on food intake. These studies have involved: (1) characterizing the changes in feeding activity due to TPN; (2) investigating the involvement of the central nervous system; and (3) investigating the role of the periphery and its metabolites in the regulation of food intake during TPN. Some insight into the mechanism of action of TPN on food intake is provided.

1. Insulin sensitivity was quantified using a modified euglycaemic technique after hepatic cholinergic blockade with atropine and compared with that after surgical denervation. 2. Intraportal administration of atropine produced dose-dependent inhibition of insulin sensitivity in glucose metabolism. ED50 of atropine was 0.99 mg kg-1 (1 mg = 1.5 microM) with maximum inhibition of 40.3 +/- 11.6%. 3. Atropine (3 mg kg-1) reduced insulin sensitivity by a similar amount (33.6 +/- 3.4%) to that produced by hepatic surgical denervation (37.8 +/- 9.8%). Doses greater than 3 mg kg-1 failed to further alter the insulin resistance produced by surgical denervation or atropine (3 mg kg-1) administration, suggesting that activation of hepatic parasympathetic nerves is necessary to fully express the insulin effect. 4. Atropine reduced insulin sensitivity without changes in plasma concentrations of glucagon or insulin. The temporal response to insulin in this euglycaemic study was not changed after atropine administration or after surgical hepatic denervation. 5. It is suggested that hepatic parasympathetic nerves show a synergistic effect with insulin. Disease states that result in hepatic parasympathetic neuropathy would be expected to produce an insulin resistant liver. 6. The modified euglycaemic clamp method for assessing insulin responses was shown to be reproducible up to four times in the same animal and was sufficiently sensitive and quantitative to be able to generate a dose-response curve in each animal for atropine-induced insulin resistance.

In male young adult Wistar rats the influences of nucleus raphe electrocoagulation, spinal cord dissection (cordotomy between C7 and Th1), vagotomy and denervation of liver hilus by phenol on liver cytochrome P450-system (cytochrome P450 concentration, ethylmorphine N-demethylation and ethoxycoumarin O-deethylation activities, hexobarbitone sleeping time) were investigated. In general the influences were small or negligible when compared with sham operated controls, only after vagotomy the depressing effect of sham operation was abolished. In all cases sham operation had a depressing effect until up to five weeks after operation.

In the liver, transcript destabilization contributes to the decrease in steady-state levels of beta 2-adrenergic receptor mRNA that occurs during early postnatal development in the rat. From genomic DNA, polymerase chain reaction (PCR) was used to amplify a 718-basepair (bp) fragment of the beta 2-adrenergic receptor gene including the entire 3'-untranslated region. Results from SDS-gel electrophoresis and autoradiography demonstrated a M(r) 85,000 cellular factor present in postnatal day 60, but not fetal day 18 rat liver that was ultraviolet (UV) light-crosslinked to in vitro transcribed beta 2-adrenergic receptor RNA 3'-untranslated region. Unlabeled beta 2-adrenergic receptor RNA 3'-untranslated region, but not mouse beta-actin RNA, competed with labeled beta 2-adrenergic receptor RNA 3'-untranslated region for binding to the M(r) 85,000 protein. Cross-linking of the beta 2-adrenergic receptor RNA 3'-untranslated region to the M(r) 85,000 protein was inhibited by the ribohomopolymer poly(U), with poly(A), poly(C) and poly(G) having little or no effect. Thus, a M(r) 85,000 protein has been identified in adult male rat liver that may interact with U-rich sequences in the 3'-untranslated region of the beta 2-adrenergic receptor mRNA and may account for the decreased stability of hepatic beta 2-adrenergic receptor gene transcripts that occurs during development.

The liver innervation of eight different mammalian species was examined by immunohistochemical localization of protein gene product (PGP) 9.5 to visualize the general innervation for autonomic nerve fibres. In addition, dopamine beta-hydroxylase (DBH) and tyrosine hydroxylase (TH), two enzymes involved in catecholamine synthesis, were localized immunohistochemically to delineate hepatic sympathetic nerve fibres. We found that: (1) Within the interlobular region of each species, PGP 9.5, DBH and TH-positive nerve fibres were all seen in close association with branches of hepatic arteries, portal veins and bile ducts. (2) Within the parenchyma of the guinea-pig, cat, dog, pig, monkey and human liver, the presence of the three immuno-positive nerve fibres could be unequivocally identified, although the density of these intralobular fibres showed marked species variation. Moreover, immunoelectron microscopic study confirmed that PGP 9.5-positive nerve terminals of the human liver are in close apposition to hepatocytes. (3) In mouse and rat, no parenchymal nerve fibres immunoreactive for PGP 9.5, TH or DBH could be demonstrated.

We examined the disposition of a mixed meal by nine conscious dogs fasted for 24 hours with surgical hepatic denervation. The results were compared with those from identical studies carried out previously in 13 hepatic-innervated dogs. Net gut release of glucose and gluconeogenic precursors (assessed with the arteriovenous difference technique), the resulting blood glucose and plasma insulin concentrations, and the hepatic glucose load were remarkably similar in the two groups. Net hepatic glucose uptake was 4.8 +/- 3.6 g in hepatic-denervated and 7.7 +/- 3.3 g in hepatic-innervated dogs. Cumulative net hepatic lactate release in hepatic-denervated dogs was 4.3 +/- 1.4 g of glucose equivalents, half the value for hepatic-innervated dogs. Net hepatic carbon intake was similar in the two groups. Hepatic lipogenesis, oxidation, and net glycogen synthesis were qualitatively similar between groups. In conclusion, the disposition of a mixed meal by hepatic-innervated and hepatic-denervated dogs was very similar. Subtle alterations in net hepatic balance of substrates (tendencies toward decreases in net hepatic glucose uptake and lactate release) made net carbon retention in denervated livers virtually identical with that in innervated livers. When other compensatory mechanisms are intact, hepatic denervation does not significantly alter hepatic disposition of a mixed meal.

The central nervous system has been implicated in the activation of counterregulatory hormone release during hypoglycemia. However, the precise loci involved are not established. To determine the role of the ventromedial hypoglycemia, we performed hypoglycemic clamp studies in conscious Sprague-Dawley rats with bilateral VMH lesions produced by local ibotenic acid injection 2 wk earlier. Rats with lesions in the lateral hypothalamic area, frontal lobe, sham operated (stereotaxic needle placement into hypothalamus without injection), and naive animals served as control groups. The clamp study had two phases. For the first hour plasma glucose was fixed by a variable glucose infusion at euglycemia (approximately 5.9 mM). Thereafter, for an additional 90 min, glucose was either allowed to fall to (a) mild hypoglycemia (approximately 3.0 mM) or (b) more severe hypoglycemia (approximately 2.5 mM). Glucagon and catecholamine responses of lateral hypothalamic area-, frontal lobe-lesioned, sham operated, and naive animals were virtually identical at each hypoglycemic plateau. In contrast, glucagon, epinephrine, and norepinephrine responses in the VMH-lesioned rats were markedly inhibited; hormones were diminished by 50-60% during mild and by 75-80% during severe hypoglycemia as compared with the other groups. We conclude that the VMH plays a crucial role in triggering the release of glucagon and catecholamines during hypoglycemia.