Gut apical amino acid (AA) transport activity is high at birth and during suckling, thus being essential to maintain luminal nutrient-dependent mucosal growth through providing AA as essential metabolic fuel, substrates and nutrient stimuli for cellular growth. Because system-B(0) Na(+)-neutral AA co-transporter (B(0)AT1, encoded by the SLC6A19 gene) plays a dominant role for apical uptake of large neutral AA including L-Gln, we hypothesized that high apical Na(+)-Gln co-transport activity, and B(0)AT1 (SLC6A19) in co-expression with angiotensin-converting enzyme 2 (ACE2) were expressed along the entire small intestinal crypt-villus axis in young animals via unique control mechanisms. Kinetics of Na(+)-Gln co-transport activity in the apical membrane vesicles, prepared from epithelial cells sequentially isolated along the jejunal crypt-villus axis from liquid formula-fed young pigs, were measured with the membrane potential being clamped to zero using thiocyanate. Apical maximal Na(+)-Gln co-transport activity was much higher (p < 0.05) in the upper villus cells than in the middle villus (by 29 %) and the crypt (by 30 %) cells, whereas Na(+)-Gln co-transport affinity was lower (p < 0.05) in the upper villus cells than in the middle villus and the crypt cells. The B(0)AT1 (SLC6A19) mRNA abundance was lower (p < 0.05) in the crypt (by 40-47 %) than in the villus cells. There were no significant differences in B(0)AT1 and ACE2 protein abundances on the apical membrane among the upper villus, the middle villus and the crypt cells. Our study suggests that piglet fast growth is associated with very high intestinal apical Na(+)-neutral AA uptake activities via abundantly co-expressing B(0)AT1 and ACE2 proteins in the apical membrane and by transcribing the B(0)AT1 (SLC6A19) gene in the epithelia along the entire crypt-villus axis.

Gut apical Na(+)-glucose cotransporter 1 (SGLT1) activity is high at the birth and during suckling, thus contributing substantially to neonatal glucose homeostasis. We hypothesize that neonates possess high SGLT1 maximal activity by expressing apical SGLT1 protein along the intestinal crypt-villus axis via unique control mechanisms. Kinetics of SGLT1 activity in apical membrane vesicles, prepared from epithelial cells sequentially isolated along the jejunal crypt-villus axis from neonatal piglets by the distended intestinal sac method, were measured. High levels of maximal SGLT1 uptake activity were shown to exist along the jejunal crypt-villus axis in the piglets. Real-time RT-PCR analyses showed that SGLT1 mRNA abundance was lower (P < 0.05) by 30-35% in crypt cells than in villus cells. There were no significant differences in SGLT1 protein abundances on the jejunal apical membrane among upper villus, middle villus, and crypt cells, consistent with the immunohistochemical staining pattern. Higher abundances (P < 0.05) of total eukaryotic initiation factor 4E (eIF4E) protein and eIE4E-binding protein 1 γ-isoform in contrast to a lower (P < 0.05) abundance of phosphorylated (Pi) eukaryotic elongation factor 2 (eEF2) protein and the eEF2-Pi to total eEF2 abundance ratio suggest higher global protein translational efficiency in the crypt cells than in the upper villus cells. In conclusion, neonates have high intestinal apical SGLT1 uptake activity by abundantly expressing SGLT1 protein in the epithelia and on the apical membrane along the entire crypt-villus axis in association with enhanced protein translational control mechanisms in the crypt cells.

The consequences of early-life nutritional programming in man and other mammalian species have been studied chiefly at the metabolic level. Very few studies, if any, have been performed in the gastrointestinal tract (GIT) as the target organ, but extensive GIT studies are needed since the GIT plays a key role in nutrient supply and has an impact on functions of the entire organism. The possible deleterious effects of nutritional programming at the metabolic level were discovered following epidemiological studies in human subjects, and confirmed in animal models. Investigating the impact of programming on GIT structure and function would need appropriate animal models due to ethical restrictions in the use of human subjects. The aim of the present review is to discuss the use of pigs as an animal model as a compromise between ethically acceptable animal studies and the requirement of data which can be interpolated to the human situation. In nutritional programming studies, rodents are the most frequently used model for man, but GIT development and digestive function in rodents are considerably different from those in man. In that aspect, the pig GIT is much closer to the human than that of rodents. The swine species is closely comparable with man in many nutritional and digestive aspects, and thus provides ample opportunity to be used in investigations on the consequences of nutritional programming for the GIT. In particular, the 'sow-piglets' dyad could be a useful tool to simulate the 'human mother-infant' dyad in studies which examine short-, middle- and long-term effects and is suggested as the reference model.

Phosphocreatine is an energy buffer and transducer in the heart, the brain and the skeletal muscle. Recently, we have demonstrated the presence of the Na+/Cl-/creatine transporter at the apical membrane of the small intestinal epithelium. Herein the ontogeny and segmental distribution of rat intestinal creatine transport activity are investigated. [14C]-Creatine uptake was measured in the jejunum and ileum of 16 day gestation foetuses, newborn, suckling, weaning, 1-, 2-, 7- and 12-month-old (adult) rats. Creatine content in amniotic fluid, in rat and commercial milk and in rat chow, was measured by HPLC. NaCl-dependent creatine uptake was maximal in newborn rats and, in all the ages tested, higher in the ileum than in the jejunum. In the latter, NaCl-dependent creatine uptake was undetectable after weaning. Kinetic studies revealed that the jejunum and ileum have the same creatine uptake system, and that maturation decreases its Vmax but not the apparent Km. Maintenance of the pups on a commercial milk diet supplemented with creatine prevented the ileal periweaning decline in creatine uptake activity, but not that in the jejunum. In 1-month-old rats, supplementation with creatine increased ileal, but not jejunal, creatine uptake. The results demonstrate for the first time that: (i) creatine uptake along the length of the small intestine is mediated by the same transport system, (ii) the activity of this transport system changes in a specific manner with maturation and (iii) these changes appear to be genetically programmed and controlled by the intestinal creatine content.

To evaluate the effect of age on sugar transport, we determined the uptake of methyl alpha-D-glucopyranoside and the abundance of the Na(+)-D-glucose cotransporter (SGLT1) in jejunal brush-border membrane (BBM) vesicles of 2-day- and 5-wk-old chickens. Methyl alpha-D-glucopyranoside transport per BBM protein was 40% lower in adults than in newly hatched chickens. This finding was matched by parallel declines in site density of SGLT1, which were detected by Western blot. The immunohistochemical study showed that SGLT1 was exclusively located in the BBM of enterocytes along the entire villus and was absent in the crypt in both age groups, and there was an 11-fold increase in the total absorptive area during development. Northern blot studies of the abundance of SGLT1 mRNA showed similar levels for the groups studied. We conclude that the age-related decline in Na(+)-dependent hexose transport per unit of BBM protein in the chicken jejunum is due to a reduction in the density of SGLT1 cotransporter and is regulated by a posttranscriptional mechanism.

Cryptosporidium parvum infection represents a significant cause of diarrhea in humans and animals. We studied the effect of luminally applied glutamine and the PG synthesis inhibitor indomethacin on NaCl absorption from infected calf ileum in Ussing chambers. Infected ileum displayed a decrease in both mucosal surface area and NaCl absorption. Indomethacin and glutamine or its stable derivative alanyl-glutamine increased the net absorption of Na(+) in infected tissue in an additive manner and to a greater degree than in controls. Immunohistochemical and Western blot studies showed that in control animals neutral amino acid transport system ASC was present in villus and crypts, whereas in infected animals, ASC was strongly present only on the apical border of crypts. These results are consistent with PGs mediating the altered NaCl and water absorption in this infection. Our findings further illustrate that the combined use of a PG synthesis inhibitor and glutamine can fully stimulate Na(+) and Cl(-) absorption despite the severe villous atrophy, an effect associated with increased expression of a Na(+)-dependent amino acid transporter in infected crypts.

Considerable progress has been made over the last decade in the understanding of mechanisms responsible for the ontogenetic changes of mammalian intestine. This review presents the current knowledge about the development of intestinal transport function in the context of intestinal mucosa ontogeny. The review predominantly focuses on signals that trigger and/or modulate the developmental changes of intestinal transport. After an overview of the proliferation and differentiation of intestinal mucosa, data about the bidirectional traffic (absorption and secretion) across the developing intestinal epithelium are presented. The largest part of the review is devoted to the description of developmental patterns concerning the absorption of nutrients, ions, water, vitamins, trace elements, and milk-borne biologically active substances. Furthermore, the review examines the development of intestinal secretion that has a variety of functions including maintenance of the fluidity of the intestinal content, lubrication of mucosal surface, and mucosal protection. The age-dependent shifts of absorption and secretion are the subject of integrated regulatory mechanisms, and hence, the input of hormonal, nervous, immune, and dietary signals is reviewed. Finally, the utilization of energy for transport processes in the developing intestine is highlighted, and the interactions between various sources of energy are discussed. The review ends with suggestions concerning possible directions of future research.

This study describes unidirectional influx of amino acids and D-glucose across the small intestinal brush-border membrane of fully weaned eight week old pigs. Influx is minimal in the duodenum and maximal in the distal and/or mid small intestine. Influx of beta-alanine, taurine and N-methyl-aminoisobutyric acid is chloride-dependent. The activation stoichiometry for taurine influx is 1.0 +/- 0.2 chloride/2.4 +/- 0.3 sodium/1 taurine. Influx of D-glucose, lysine, glycine and glutamate is chloride-independent. An ABC test demonstrates a common beta-amino acid carrier: (a) the apparent affinity constant K1/2Taurine is 44 +/- 13 microM (means +/- S.D.) and the inhibitory constant (KiTaurine) against beta-alanine influx is 41 +/- 5 microM (means +/- S.E.). (b) K1/2beta-alanine is 97 +/- 23 microM and Kibeta-alanine against taurine influx is 160 +/- 22 microM. (c) KiHypotaurine against taurine and beta-alanine influx is 43 +/- 4 (n = 7) and 22 +/- 5 microM (n = 7), respectively. In conclusion, a high affinity, low capacity, sodium- and chloride-dependent carrier of beta-amino acids is present in pig small intestine.

Glucose uptake into jejunal brush border membrane (BBM) varies along the crypt-villus axis (CVA). In the present study, the question was addressed whether uptake of the essential long-chain fatty acid linoleic acid also varies along the CVA. Using agitation techniques, five jejunal enterocyte fractions were sequentially isolated from female New Zealand white rabbits. A sixth and final fraction of lower-villus/crypt cells was obtained by the scraping of the remaining jejunal mucosa. Cell fraction along the CVA was proven histologically, by noting decreasing alkaline phosphatase activities in sequentially isolated fractions, and by demonstrating [3H-methyl]thymidine uptake mainly in the final fraction of the lower villus/crypt cells. BBM vesicles were prepared from the upper, mid- and lower-villus/crypt enterocyte fractions, using differential centrifugation and divalent ion precipitation. D-Glucose uptake into each fraction showed an Na(+)-gradient dependent time-course "overshoot" with linear uptake to 15 s and a subsequent decline to a steady-state plateau. Varying D-glucose concentrations from 50-1000 microM demonstrated saturation kinetics of uptake, with maximal transport rates (Vmax) and Michaelis affinity constants (Km) varying between fractions; the Km and Vmax were both lowest in the upper-villus fraction. A linear relationship existed between linoleic acid concentration (25-200 microM) and uptake in each fraction. Linoleic acid uptake was equivalent in all fractions when expressed per mg protein, but when expressed in terms of the estimated minimal BBM, vesicle surface area uptake was greater in the upper- than in the lower-villus/crypt fractions. Thus, BBM vesicle uptake of both linoleic acid and glucose vary along the crypt-villus axis of the rabbit jejunum.

The mechanisms involved in the increased Na(+)-dependent nutrient uptake across intestine of diabetic animals are poorly understood. Here we have studied the effect of acute (7d) and chronic (30-40d) diabetes on the autoradiographic localization of 3H-L-valine accumulation by rat jejunal villi and on enterocyte migration rate. In control rats, Na(+)-dependent valine uptake was confined to enterocytes on the upper 20-23% of the villus. In intestine from diabetic rats, however, this area was extended to occupy the upper 42-45% of an enlarged villus surface. Hyperphagia was not responsible for the expanded functional surface and systemic factors are therefore implicated in the adaptive response. Enterocyte migration rate was found to be unaffected by diabetes but an increased villus height in this condition resulted in an additional 13.5 h in enterocyte lifespan. These data are compatible with the hypothesis that during diabetes the earlier maturation of enterocyte absorptive function produces an epithelial surface containing a higher proportion of mature enterocytes.

This study examined jejunal sugar absorption in piebald mice with congenital megacolon and in normal littermates. Transmural potential difference, short-circuit current, and tissue conductance of flat sheets of jejunum set up in flux chambers were significantly greater in the diseased mice compared to normal siblings. In piebald mice, net absorption of 3-o-methylglucose was enhanced due to a significant increase in mucosal-to-serosal flux compared with normal littermates. Stimulation of electrogenic sodium absorption by alanine (10 mM) increased basal short-circuit currents more in piebald tissues than in tissues from normal mice, whereas stimulation of ion transport by carbachol (10 microM) evoked an increase in short-circuit current that was similar in the two groups. Alterations in intestinal mass, morphology, or Na+, K+-ATPase activity could not account for the increase in absorptive function characteristic of piebald mice.

1. In the newborn pig it appears that only prenatally produced enterocytes are capable of absorbing large amounts of protein. 2. The ability of the small intestine to transport sodium, lysine, lysine containing dipeptides and glucose declines markedly during the first week of post natal life. 3. Dexamethosone causes a doubling of the sodium dependent portion of alanine uptake. 4. EGF given between days three and six of postnatal life increases sucrase and maltase activity in the distal region of the small intestine. 5. Weaning induced problems are probably not due to direct inhibition of transport properties.

We report here the effects of a 72-h fast on the localisation of Na-dependent [3H]-valine uptake by rat small intestine. Starvation results in the earlier appearance of valine transport during cell migration and an enhanced accumulation of the amino acid at the villus tip.

Isocal, but not Portagen, is associated with increased villus surface area in control rabbits and in animals with an ileal resection. In control animals, Isocal feeding was associated with an increased in vitro jejunal uptake of short and medium-chain length fatty acids and cholesterol, whereas Portagen feeding was associated with a decline in the uptake of short-, medium- and long-chain fatty acids, but an increase in the uptake of cholesterol. In animals with an ileal resection both diets were associated with an increased uptake of long-chain fatty acids and cholesterol. These changes in lipid uptake are not explained by alterations in villus surface area or unstirred water layer resistance.

Positional and temporal correlates for the development of microvillus membranes and for two of the hydrolytic enzymes they contain have been determined and compared with the ability of enterocytes to transport valine during migration from crypt base to villus tip in jejunal tissue taken from rats maintained on diets containing different amounts of protein. Microvillus elongation and the appearance of both aminopeptidase N (APN) and isomaltase (IM) activities reached maximal rates of expression in enterocytes located 16 +/- 5 micron from the crypt-villus junction. This close positional correlation was not found for the later development of the valine transport function. Feeding rats isoenergetic diets containing 20% instead of 5% protein caused significant increases in both villus height and crypt depth without changing the positional correlations described above. The maximal rates for microvillus elongation and APN and IM appearance were greater and occurred earlier in enterocytes taken from rats fed a high-protein diet. The time of onset and capacity to transport valine were found to be closely correlated for rats maintained on high- and low-protein diets. The ratio of APN to IM activity in fully differentiated enterocytes was either 0.7 or 1.2 depending on whether rats had been fed a low- or high-protein diet. The maximal length of microvillus membranes in fully differentiated enterocytes from rats on a low-protein diet was 1.4 times that found in rats maintained on a high-protein diet. Possible ways in which the microvillus membrane structure of enterocytes, enzyme activity and the ability to transport amino acids might be controlled are discussed. Relative estimates are also made of the probable effects that changes in diet will have on the capacity of the intestine to digest and absorb nutrients.

A positional analysis of enterocyte membrane potential has been carried out using in vitro preparations of rabbit distal ileum. Young enterocytes were found to possess a microvillar membrane potential significantly less than that seen in older enterocytes. The length of enterocyte microvilli was also found to be significantly less in younger enterocytes. It is suggested that developmental changes in membrane potential, occurring during the early stages of enterocyte differentiation, probably reflect a changed permeability to ions associated with the establishment of a fully developed microvillar membrane. Other explanations for the observed findings are also considered.