As the potential of pluripotent stem cell-derived differentiated cells has been demonstrated in regenerative medicine, differentiated vascular endothelial cells (ECs) are emerging as a therapeutic agent for the cardiovascular system. To verify the therapeutic efficacy of differentiated ECs in an ischemic model, human embryonic stem cells (hESCs) are induced as EC lineage and produce high-purity ECs through fluorescence-activated cell sorting (FACS). When hESC-ECs are transplanted into a hindlimb ischemic model, it is confirmed that blood flow and muscle regeneration are further improved by creating new blood vessels together with autologous ECs than the primary cell as cord blood endothelial progenitor cells (CB-EPCs). In addition, previously reported studies show the detection of transplanted cells engrafted in blood vessels through various tracking methods, but fail to provide accurate quantitative values over time. In this study, it is demonstrated that hESC-ECs are engrafted approximately sevenfold more than CB-EPCs by using an accelerator mass spectrometry (AMS)-based cell tracking technology that can perform quantification at the single cell level. An accurate quantification index is suggested. It has never been reported in in vivo kinetics of hESC-ECs that can act as therapeutic agents.

To analyze the effects of NF- kappa B inhibition by antioxidant pyrrolidine dithiocarbamate (PDTC) or TNF inhibitor pentoxifylline (PTX) on liver regeneration after partial hepatectomy (PH).

Saline, PDTC or PTX were injected 1 h before PH and rats were killed at 0.5 and 24 h after PH. Several control groups were used for comparison (injection control groups).

Compared to saline injected controls, NF- kappa B activation was absent 0.5 h after PH in rats treated with PDTC or PTX. At 24 h after PH, DNA synthesis and PCNA expression were identical in treated and control rats and thus occurred irrespectively of the status of NF- kappa B activation at 0.5 h. Signal transducer and activator of transcription 3 (Stat3) activation was observed already 0.5 h after PH in saline, PDTC or PTX group and was similar to Stat3 activation in response to injection without PH.

These data strongly suggest that (1) NF- kappa B p65/p50 DNA binding produced in response to PH is not a signal necessary to initiate the liver regeneration, (2) Stat3 activation is a stress response unrelated to the activation of NF- kappa B. In conclusion, NF- kappa B activation is not critically required for the process of liver regeneration after PH.

The aim of the study was to determine whether hepatic regeneration stimulates growth of tumour residing within the liver, and whether a difference in the rate of DNA synthesis in liver and tumour may be used to target cancer using the radiolabelled thymidine analogue 5-iodo-2'-deoxyuridine (IUdR).

Partial hepatectomy was performed on Buffalo rats bearing solitary nodules of syngeneic Morris hepatoma. Liver and tumour DNA synthesis was measured by incorporation of radioactive IUdR. [(125)I]IUdR was tested as an adjuvant therapy after hepatectomy in Buffalo rats bearing diffuse microscopic Morris hepatomas to simulate the clinical situation.

Liver regeneration enhanced liver and tumour DNA synthesis as measured by incorporation of radioactive IUdR. Liver DNA synthesis returned to baseline by 7 days, whereas tumour DNA synthesis remained above baseline level. Hepatectomy enhanced the growth of microscopic liver tumours. [(125)I]IUdR (250 micro Ci or 1 mCi/kg) administered 4 days after hepatectomy significantly reduced tumour growth without signs of systemic toxicity or liver dysfunction.

The local environment of the regenerating liver stimulates tumour growth. The thymidine analogue [(125)I]IUdR may be used preferentially to target tumour DNA synthesis in the regenerating liver, and may prove useful as an adjuvant therapy for hepatic tumours after surgical resection.

The origins of positron emission tomography (PET) date back 70 years. Since the 1970s, however, its use has increased exponentially in the fields of neurology, cardiology and oncology. [18F]-Fluorodeoxyglucose (FDG) whole-body scanning is by far the most widely utilised and recognised application of PET in oncology. However, PET is a very versatile and powerful imaging modality capable of helping bridge the gap between the laboratory and the clinic. This article reviews the history and current applications of PET in oncology and then explores some of the newer applications and potential future uses of this versatile technology particularly in the area of cancer research.

Two glycopeptides were synthesized by attaching purified glycosylamines (N-glycans) to a 20 amino acid peptide. Triantennary and Man9 Boc-tyrosinamide N-glycans were treated with trifluoroacetic acid to remove the Boc group and expose a tyrosinamide amine. The amine group was coupled with iodoacetic acid to produce N-iodoacetyl-oligosaccharides. These were reacted with the sulfhydryl group of a cysteine-containing peptide (CWK18), resulting in the formation of glycopeptides in good yield that were characterized by 1H NMR and ESIMS. Both glycopeptides were able to bind to plasmid DNA and form DNA condensates of approximately 110 nm mean diameter with zeta potential of +31 mV. The resulting homogeneous glycopeptide DNA condensates will be valuable as receptor-mediated gene-delivery agents.

2-[11C]Thymidine has been produced from [11C]methane via [11C]phosgene and [11C]urea. Anhydrous [11C]urea was prepared from [11C]phosgene by reaction with liquid ammonia. This novel approach avoids the problems associated with the synthesis of anhydrous [11C]urea from [11C]cyanide. A fully automated system based on a modular approach and under PLC control has been developed. The system provides 2-[11C]thymidine reliably and reproducibly for clinical PET studies. The radiosynthesis takes 45-50 min from [11C]methane and the average yield was 1.5-3.3 GBq (40-90 mCi). The specific radioactivity was typically in the range 29.6-51.8 GBq mumol-1 (0.8-1.4 Ci mumol-1) at EOS corresponding to 6-12 micrograms of stable thymidine. The radiochemical yield of 2-[11C]thymidine was ca. 14% from [11C]methane.

We employed quasielastic and static light scattering to measure apparent values of the mean hydrodynamic radii (Rh)app, molecular weights (Mapp), and radii of gyration (Rg)app in solutions containing mixed micelles composed of bile salts (cholate and taurochenodeoxycholate, both cholanoyl derivatives) and the glycoacyl chain detergent, octyl glucoside, with egg yolk phosphatidylcholine (EYPC) as functions of total lipid concentration (0.1-10 g/dL), EYPC/detergent molar ratio (0-1.2), and ionic strength (0.15-0.4 M NaCl) at 20 degreesC and 1 atm. As the mixed micellar phase boundaries were approached by dilution, (Rh)app, Mapp, and (Rg)app values increased markedly by up to 20-fold. For each micellar system, the scaling ratios (Rh)app/Mapp1/2 and (Rg)app/(Rh)app remained essentially constant at 0.018 nm/(g/mol)1/2 and 1.5 (dimensionless), respectively, despite large variations in total lipid concentration, detergent molecular species, and ionic strength. Refined data analysis is inconsistent with a flat "mixed-disc" model for bile salt-EYPC micelles [Mazer, N. A., Benedek, G. B., and Carey, M. C. (1980) Biochemistry 19, 601] and octyl glucoside-EYPC micelles principally because the numerical value of (Rh)app/Mapp1/2 corresponds to a hypothetical disk thickness of approximately 1 nm, which is 4-fold smaller than the bimolecular width of EYPC molecules, and for a disk, (Rg)app/(Rh)app ratios should be close to 1 at low total lipid concentrations. Assuming disc-shaped micelles, we show that intermicellar excluded volume interactions would have only a minor effect on Mapp and cannot account for the unrealistic disk thickness. Instead, locally cylindrical, semiflexible wormlike micelles of diameter d = 4 nm and persistence length xip = 17 nm in solution are compatible with the observed (Rh)app/Mapp1/2 and (Rg)app/(Rh)app values when intermicellar excluded-volume interactions are considered. With EYPC/taurochenodeoxycholate = 0.6 and EYPC/cholate = 1.0 in 0.15 M NaCl, independent micelles grow upon dilution and use of the second virial coefficient [Egelhaaf, S. U., and Schurtenberger, P. (1994) J. Phys. Chem. 98, 8560] is adequate for estimating micellar weights. The systems EYPC/cholate = 1.0 in 0.4 M NaCl, EYPC/cholate = 1.2 in 0.15 M NaCl, and EYPC/octyl glucoside = 0.13 in 0.15 M NaCl all form highly overlapping, semidilute polymer solutions, which mimic the observed scaling ratios. In such semidilute systems, use of the second virial coefficient alone to account for intermicellar interactions is inadequate for estimating micellar weights. The results of the present study, in combination with locations of known phase boundaries of the ternary bile salt-EYPC-water phase diagram at high dilution, suggest that elongation, as well as entanglement of wormlike mixed micelles may occur at concentrations approaching the micellar phase limit.

The intermixed micellar/intervesicular bile salt (BS) concentration (IMC), composed of BS monomers and simple micelles, is in dynamic equilibrium with mixed micelles and vesicles. Accurate separation of biliary lipid aggregates is believed to depend on accurately measuring the IMC. Using centrifugal ultrafiltration, we measured the IMC of cholesterol-supersaturated model biles that were physiologically composed. Gel chromatography was performed using eluants containing the following: 1) the IMC; 2) the same BS composition as the IMC but higher or lower BS concentrations; 3) the same BS concentration as the IMC, but with more hydrophilic or hydrophobic BS; and 4) 10 mmol/L cholate. Compared with an eluant containing the same BS composition as the IMC, an eluant containing the same relative BS composition but 75% of the IMC increased the proportion of cholesterol in vesicles and decreased the vesicular cholesterol/egg yolk phosphatidylcholine (EYPC) ratio. In contrast, an eluant containing 150% of the IMC entirely transformed vesicles to micelles. Eluants containing slightly more hydrophobic or more hydrophilic BS eliminated or increased vesicular cholesterol content, respectively. An eluant of 10 mmol/L cholate overestimated vesicular cholesterol and in concentrated biles reproducibly produced an incompletely separated intermediate peak, possibly because of re-equilibration between mixed micelles and vesicles. Further, in concentrated biles, fractions eluting at volumes corresponding to mixed micelles were visibly turbid, irrespective of the eluant used. The correct IMC allows accurate separation of biliary lipid aggregates, but differences in BS concentration or composition substantially alter the vesicular percentage of cholesterol as well as the cholesterol/EYPC ratio. Elution with 10 mmol/L cholate may introduce artifactual gel-filtration peaks and inadequate separation of particles with widely differing molecular weights, both of which have confused previous analyses of biliary lipid aggregates.

Galactosyltransferase, sialyltransferase, and fucosyltransferase were used to create a panel of complex oligosaccharides that possess multiple terminal sialyl-Le(x) (NeuAc alpha 2-3Gal[Fuc alpha 1-3] beta 1-4GlcNAc) and GalNAc-Le(x) (GalNAc[Fuc alpha 1-3]beta 1-4GlcNAc). The enzymatic synthesis of tyrosinamide biantennary, triantennary, and tetraantennary N-linked oligosaccharides bearing multiple terminal sialyl-Le(x) was accomplished on the 0.5 mumol scale and the purified products were characterized by electrospray MS and 1H NMR. Likewise, biantennary and triantennary tyrosinamide oligosaccharides bearing multiple terminal GalNAc-Le(x) determinants were synthesized and similarly characterized. The transfer kinetics of human milk alpha 3/4-fucosyltransferase were compared for biantennary oligosaccharide acceptor substrates possessing Gal beta 1-4GlcNAc, GalNAc beta 1-4GlcNAc, and NeuAc alpha 2-3Gal beta 1-4GlcNAc which established NeuAc alpha 2-3Gal beta 1-4GlcNAc as the most efficient acceptor substrate. The resulting complex oligosaccharides were chemically tethered through the tyrosinamide aglycone to the surface of liposomes containing phosphatidylthioethanol, resulting in the generation of glycoliposomes probe which will be useful to study relationships between binding affinity and the micro- and macro-clustering of selectin ligand.

To examine the role of the early changes occurring in the liver within the first hours after a partial hepatectomy and in an attempt to demonstrate the involvement of subsequent regulatory mechanisms, the size of the remnant liver was modified at various times and by different surgical techniques. Male Wistar rats were submitted to a two-thirds "temporary partial hepatectomy" produced by a 3-h occlusion of the pedicle of the anterior lobes protected by local hypothermia. Various indexes of cell proliferation ([3H]thymidine uptake and 5-bromo-2'-deoxyuridine and proliferating cell nuclear antigen labeling) were not increased despite a c-myc expression as high as that observed after a two-thirds partial hepatectomy. The temporary partial hepatectomy and a sham operation induced modifications of the hepatocytes, allowing rapid DNA synthesis after a subsequent two-thirds partial hepatectomy. After this initial nonspecific response, the extent of the regenerative response is determined according to the size of the liver mass present approximately from the 10th to the 18th hour after the initial stimulus. For instance, when a one-third partial hepatectomy was converted into a two-thirds partial hepatectomy at the 10th hour, the DNA synthesis at the 24th hour reached the value observed after a straightforward two-thirds partial hepatectomy. Inversely, the regenerative response was significantly reduced when additional liver lobes were connected to neck vessels between the 14th and the 18th hour after a two-thirds partial hepatectomy. In conclusion, the actual liver mass present during the period corresponding to mid- to late G1 appears to control the magnitude of the proliferative response, which is not the simple consequence of the early changes following a partial hepatectomy.

Liver regeneration is an essential component of the reparative process following liver injury and surgical resection. It can be assessed by different tissue-based tests such as liver weights, mitotic counts, DNA contents and synthesis rates, immunohistochemical staining of nuclear antigens, gene expressions and certain protein levels or various serum-based tests that largely consist of specific enzyme determinations or documentation of certain proliferation markers. Although the simplest tissue-based test of liver regeneration is measurement of liver weights, these determinations are influenced by the extent of deposition of various materials not directly related to regeneration, such as lipids, glycogen and blood volumes. Because mitosis constitutes a very short segment of the cell cycle, mitotic counts are infrequently observed by light microscopy. Thymidine and BrdU incorporation into DNA are the reference tools for studying DNA synthesis, but their use requires pre-injection with radioactive isotopes or nucleotides which render them impractical for human studies. Flow cytometry is an accurate and objective method of monitoring hepatic regenerative activity but requires sophisticated equipment that is not generally available in many laboratories. Immunohistochemical staining for nuclear antigens (Ki-67, proliferating cell nuclear antigen [PCNA], DNA polymerase alpha and nucleolar organizer region [NOR] proteins) are acceptable and commonly used methods of monitoring regenerative activity but are subject to inter- and intra-observer variability. Gene expression rates such as Histone-3 mRNA abundance are hampered by the relatively low rates of gene transcription and the need for recombinant DNA technology. Protein and enzyme levels in liver tissues, such as putrescine, ornithine decarboxylase and thymidine kinase, are not precise and are confounded by the nutritional status of the host. While PCNA protein levels measured by immunoblot hold promise as a simple, accurate and reproducible marker of liver regeneration, additional studies are required to determine if this is a valid marker of regenerative activity in various models of hepatic injury and in humans. Of the serum-based determinations: thymidine kinase, ornithine decarboxylase, fibronectin, alpha fetoprotein, and early pregnancy factor offer practical and non-invasive tools to monitor liver regeneration, but the sensitivity and specificity of these tests have yet to be determined. In conclusion, many tissue and serum-based methods have been employed in clinical and experimental studies to assess liver regeneration; however, a gold standard has yet to be identified. Because of the disadvantages inherent in each method, and until a new, more accurate marker is identified, clinicians and scientists should incorporate a minimum of two independent markers in studies of liver regeneration.

In previous studies we have shown the ability of bile acids to reduce the rate of thymidine incorporation into DNA by the regenerating rodent liver. The aim of the present work was to investigate the sensitivity of the key pathways involved in thymidine metabolism to taurocholate.

Incubation of [14C]-thymidine with mouse liver extracts revealed that addition of taurocholate to the reaction medium induced significant dose-dependent inhibition in the activity of the salvage nucleotide pathway rate-limiting enzyme, thymidine kinase, while other steps of nucleotide metabolism machinery, such as the rate-limiting enzyme of de novo deoxyribonucleotide synthesis, ribonucleotide reductase and the rate-limiting enzyme of thymidine catabolism, dihydropyrimidine dehydrogenase were found to be insensitive to inhibition by taurocholate. Additional experiments were carried out on isolated perfused rat livers whose regeneration was induced by two-thirds hepatectomy and synchronized by intravenous administration of reversible ribonucleic reductase inhibitor hydroxyurea (bolus: 170 mumol/100 g body weight, plus 10 h infusion: 2.0 mumol/min per 100 g body weight, from 14 to 24 h after hepatectomy). Hydroxyurea treatment was interrupted and liver perfusions were carried out 0, 2, 4 or 8 h later. Thymidine incorporation into DNA over 30 min perfusion with media containing [14C]-thymidine was measured after separating DNA from acid-soluble fraction. A marked increase in DNA synthesis was observed up to 4 h after stopping ribonucleotide reductase inhibition. At this time, reduced relevance of the salvage pathway can be expected as compared with the de novo released pathway. In contrast with the inhibitory effect observed when taurocholate was added to the perfusate of untreated regenerating livers, taurocholate was found to have no effect on DNA synthesis, at the peak of synchronized DNA synthesis, although taurocholate-induced alteration in thymidine metabolism was suggested from h.p.l.c. analysis of acid-soluble fraction.

These results suggest that effects on the nucleotide metabolism machinery, and hence changes in deoxyribonucleotide phosphate pools may underlie the ability of taurocholate to affect DNA synthesis by the regenerating rodent liver.

Bile salts have been hypothesized to mediate cytotoxicity by increasing membrane permeability to aqueous solutes. We examined whether submicellar bile salt concentrations affect model and native membrane permeability to small uncharged molecules such as water, urea, and ammonia. Osmotic water permeability (Pf) and urea permeability were measured in large unilamellar vesicles composed with egg yolk phosphatidylcholine (EYPC) +/- cholesterol (Ch) or rat liver microsomal membranes by monitoring self-quenching of entrapped carboxyfluorescein (CF). Ammonia permeability was determined utilizing the pH dependence of CF fluorescence. Submicellar bile salt concentrations did not significantly alter Pf of EYPC +/- Ch or rat liver microsomal membranes. At taurodeoxycholate (TDC) or tauroursodeoxycholate concentrations approaching those that solubilized membrane lipids, CF leakage occurred from vesicles, but Pf remained unchanged. Higher bile salt concentrations (0.5-2 mM TDC) did not alter Pf of equimolar EYPC/Ch membranes. The activation energy for transmembrane water flux was unchanged (12.1 +/- 1.2 kcal/mol for EYPC) despite the presence of bile salts in one or both membrane hemileaflets, suggesting strongly that bile salts do not form transmembrane pores that facilitate water flux. Furthermore, submicellar bile salt concentrations did not increase membrane permeability to urea or ammonia. We conclude that at submicellar concentrations, bile salts do not form nonselective convective channels that facilitate transmembrane transport of small uncharged molecules. These results suggest that bile salt-mediated transport of specific substrates, rather than nonselective enhancement of membrane permeability, underlies bile salt cytotoxicity for enterocytes and hepatocytes.

Bile acids have been reported to modify DNA synthesis by rodent livers in regeneration, which may be due in part to their ability to interact with the machinery responsible for deoxyribonucleotide synthesis. The aim of this work was to gain information on the effect of taurocholate (TC) on both anabolic and catabolic pathways accounting for the fate of [methyl-14C]thymidine in the liver of two-third hepatectomized rats. Using high-pressure liquid chromatography, the soluble fraction of liver homogenate was used to measure the ability of TC to modify both the rate of thymidine monophosphate formation from thymidine - i.e., thymidine kinase (TK) activity - and the rate of thymidine release from thymidine, which is the result of at least three different reactions catalyzed by thymidine phosphorylase, nucleosidase and nucleoside deoxyribosyl transferase. TC was found to induce a dose-dependent inhibition of both processes. The nature of this inhibition seems to be in part competitive. Apparent Ki values were 1.5 mM for TK and 4 mM for thymidine release. These inhibitory effects were mimicked by glycocholate but not by taurine. To investigate the relevance of the TC-induced modification of anabolism and catabolism in the whole organ, experiments on regenerating perfused rat livers were carried out. The donors underwent two-third hepatectomy 24 h before liver isolation. They were either fasted during this period (F) or allowed free access to food (NF). DNA synthesis, as measured by [methyl-14C]thymidine incorporation into DNA, was significantly increased in both groups, as compared with control non-hepatectomized animals. However, enhancement in DNA synthesis in group F was only 50% of the value found in the NF group. Intravenous TC administration before and/or during liver perfusions induced a dose-dependent recovery of DNA synthesis in the F group. This effect was accompanied by opposed modifications in the amount of radiolabelled metabolites contained in the non-DNA fraction of liver homogenate, consistent with a marked inhibition of thymidine catabolism. These results suggest that, in addition to the previously reported effects of TC on thymidine anabolism, bile acids are also able to affect the thymidine catabolism. The overall results of this dual effect on the fate of thymidine in the regenerating rat liver depend on the metabolic situation. Under circumstances of no nutrient restriction, the effect of TC is characterized by inhibition of thymidine incorporation into DNA. By contrast, under depressed DNA synthesis due to fasting, the overall effect of TC is a partial recovery of this process.

Using model systems, we explored a potential function of hepatic phosphatidylcholine transfer protein to extract biliary-type phosphatidylcholines from intracellular membranes (e.g., smooth endoplasmic reticulum) and deliver them to canalicular plasma membranes where biliary secretion occurs. We measured transfer rates of parinaroyl phosphatidylcholine, a naturally fluorescent phospholipid, from small unilamellar vesicles composed of sn-1 palmitoyl, sn-2 parinaroyl phosphatidylcholine, and egg yolk phosphatidylcholine (molar ratio 75:25) wherein the fluorophore is self-quenched to small unilamellar vesicles composed of phosphatidylethanolamine, sphingomyelin, phosphatidylserine, phosphatidylinositol, and cholesterol (molar ratios 22:22:10:8:38) representing model microsomal and canalicular plasma membranes, respectively. Following addition of phosphatidylcholine transfer protein (purified from bovine liver), fluorescence intensity increased exponentially indicating net phosphatidylcholine transfer from donor to acceptor vesicles. Submicellar concentrations of a wide hydrophobicity range of common and uncommon taurine and glycine conjugated bile salts species (anionic steroid detergent-like molecules), sodium taurofusidate (a conjugated fungal bile salt analog), and sodium dodecyl sulfate and octylglucoside, anionic and nonionic straight chain detergents, respectively, markedly stimulated phosphatidylcholine transfer protein activity. This 40-115-fold effect was most pronounced for the common bile salts and correlated positively with bile salt hydrophobicity. Thermodynamic analysis of net transfer revealed that the rate-limiting step was extraction of phosphatidylcholine molecules from donor vesicles and that bile salts facilitated their capture by enhancing both phosphatidylcholine transfer protein binding as well as perturbing phospholipid packing in vesicle bilayers.(ABSTRACT TRUNCATED AT 250 WORDS)

The evolution of microstructures present in human gallbladder and hepatic bile was observed simultaneously by video-enhanced light microscopy (VELM) and transmission electron microscopy of vitrified specimens (cryo-TEM), as a function of time after withdrawal from patients. Fresh centrifuged gallbladder bile samples contained small (6 nm) spherical micelles in coexistence with vesicles (40 nm). Out of the seven bile samples investigated four contained, in addition, two types of elongated aggregates that have not been previously described. Uncentrifuged gallbladder bile also contained a mixture of ribbon- and plate-like crystals seen by VELM, but not by cryo-TEM. In aged (3-6-week-old) gallbladder bile samples VELM also revealed spiral and helical crystal structures. No such crystals were present in hepatic bile samples, although microcrystals, not observable by VELM were seen by cryo-TEM in addition to micelles and vesicles. The similarity of these observations to those observed in bile models lends strong support for the validity of the model systems. Furthermore, the presence of microcrystals in hepatic bile samples, apparently devoid of crystals by light microscopy, indicates that under certain conditions the common criterion of 'nucleation time' (NT), based on light microscopy, does not represent the real time of nucleation. In the human bile samples investigated in this study the dissociation between NT and the time of observation of microcrystals was seen in hepatic but not in gallbladder bile samples. Hence, crystal growth may be rate limiting only in dilute biles.

The feasibility of liver regeneration determination with [2-11C]thymidine and positron emission tomography was investigated in partially hepatectomized rats. Serial tomographic scans were performed over a 120-minute period after injection of [2-11C]thymidine together with tritium-labeled thymidine. Within 10 minutes after injection, positron emission tomography scans showed a twofold higher hepatic uptake in regenerating than in nonregenerating livers. Time-activity curves over the liver area indicated that the maximal uptake was followed by a faster decrease of 11C radioactivity in controls than in regenerating animals, so that total 11C activity remaining in the liver at 120 minutes accounted for 68% of maximum in regenerating and only 38% in controls. Tissue distribution studies performed at 120 minutes showed that total 11C radioactivity, expressed in percent injected dose per gram, was six times higher in regenerating livers than in controls (0.62% +/- 0.07% in regenerating livers and 0.10% +/- 0.03% in nonregenerating livers; P less than 0.001) and correlated with 3H radioactivity measured in the nuclear fraction (r = 0.92; P less than 0.001). When the hepatic uptake was expressed in percent of dose per organ, the difference between both groups increased (2.31% +/- 0.23% in regenerating livers and 0.29% +/- 0.02% in nonregenerating livers; P less than 0.001) because of higher weight of regenerating livers than of nonregenerating livers (3.83 +/- 0.11 g in regenerating livers and 2.96 +/- 0.16 g in nonregenerating livers; P less than 0.001). In other organs examined, no difference in 11C radioactivity was found between the two groups of rats. These results indicated the potential usefulness of [2-11C]thymidine and positron emission tomography for noninvasive measurement of liver regeneration.

A three-step synthesis of [2-11C]thymidine, using [11C]urea as precursor, is described. [2-11C]Thymine was obtained by cyclization of [11C]urea and diethyl beta-methylmalate in fuming sulfuric acid. After purification of the reaction mixture, [2-11C]thymine and 2'-deoxyribose-1-phosphate were incubated in the presence of thymidine phosphorylase to form [2-11C]thymidine. The whole synthesis procedure, including purification and pharmaceutical package, was achieved within 60 min with a decay corrected yield of 30-35%.