Hepatic Urea Production Research Articles

271-OR: Hepatic Glucagon Resistance in Mice with Nonalcoholic Fatty Liver Disease

Patients with nonalcoholic fatty liver disease (NAFLD) have elevated fasting levels of glucagon (gcg) and amino acids (AA) . Gcg regulates hepatic AA catabolism by augmenting ureagenesis. We hypothesized that hepatic steatosis causes gcg resistance and impaired gcg-induced hepatic ureagenesis. To address this, we developed an isolated liver perfusion model in mice and used it to investigate gcg’s direct effect on hepatic glucose production (HGP) and ureagenesis in 9 male mice with hepatic steatosis (NAFLD mice) (B6.Vlepob/ob/JRj) and healthy controls (CON) (C57bl6/JRj) . NAFLD mice had higher body mass (50 vs. 26 g, P<0.0001) and higher hepatic fat triglycerides (1vs. µmol/g, P<0.0001) compared to CON. Catheters were place in the portal vein and the inferior vena cava and the liver was perfused with Krebs Henseleit buffer with and without 5 mM AA mixture (Vamin) , nM gcg or both. Samples were collected every minute and analyzed for urea and glucose concentrations. Results were normalized to liver tissue protein content. AA administration increased hepatic urea production from baseline in both groups within six minutes (NAFLD mice: 2.4 vs. 5.3 mmol/min × µg protein, P=0.01) , (CON: 3.4 vs. 7.4 mmol/min × µg protein, P=0.02) . Gcg increased the AA-stimulated ureagenesis compared to AA administration alone in CON (7.4 vs. 9.4 mmol/min × µg protein, P<0.0001) but not in NAFLD mice (5.3 vs. 5.1 mmol/min × µg protein, P=0.66) . During the gcg administration (50 minutes) the total HGP was far greater in CON compared to NAFLD mice (309.5 vs. 195.5 µmol/min/µg protein, P=0.03) . The difference in glucose output could not be explained by hepatic glycogen content, as the NAFLD mice showed higher glycogen content than CON (1.7 vs. 0.8 µg/mg liver mass, P=0.02) . Our data support 1) that glucagon acutely increases the substrate-induced ureagenesis and 2) that hepatic steatosis causes resistance to the acute metabolic actions of glucagon on ureagenesis. Disclosure F.R.Ceutz: None. E.E.Christensen: None. M.Winther-soerensen: None. H.Vilstrup: None. J.J.Holst: Advisory Panel; Novo Nordisk, Board Member; Antag Therapeutics, Bainan Biotech. N.J.Wewer albrechtsen: Research Support; Mercodia AB, Novo Nordisk, Regeneron Pharmaceuticals Inc., Speaker's Bureau; Merck & Co., Inc., Mercodia AB. Funding Nicolai J. Wewer Albrechtsen were financed by NNF Excellence Emerging Investigator Grant – Endocrinology and Metabolism (Application No. NNF19OC0055001) , EFSD Future Leader Award (NNF21SA0072746) and DFF Sapere Aude.

Stiffness Induces NAFLD‐like Metabolic Dysfunction in Primary Hepatocytes

BackgroundNon‐alcoholic fatty liver disease (NAFLD), the liver manifestation of the metabolic syndrome linked to obesity and insulin resistance, affects 25% of the general population both in western and developing countries. The development and progression of NAFLD is mediated by increase in lipid accumulation and triglycerides levels, excessive oxidative stress and inflammation that in turn exacerbates the diseased condition and impairs metabolic parameters. NAFLD progression is also characterized by liver stiffness due to extensive remodeling of the extracellular matrix. The role of matrix stiffness as related to subtle but pivotal changes in hepatocytes physiology and metabolic dysfunction is under explored. The overall goal of our study is the development and implementation of a platform that enables the convergence of engineered cell microenvironments with the phenotypic and functional analysis of hepatocytes. Using our innovative biomimetic liver fibrosis model that allows modulation of substrate stiffness, we investigated the role of liver matrix stiffness in modulating hepatocytes metabolic function in fibrotic‐like microenvironment.Materials and MethodsPrimary hepatocytes were cultured on our novel polymer film coated polydimethylsiloxane (PDMS) gels with 2 kPa, 9 kPa 25 kPa and 55 kPa elastic modulus mimicking healthy, early fibrotic, fibrotic and extremely fibrotic substrates. A wide range of functional/metabolic analysis were performed to determine: lipogenic and oxidation genes, glutathione expression, dynamics by Western Blot; Respirometry by Seahorse XFe24 Analyzer.ResultsWe demonstrated that stiffness impedes hepatic urea and albumin production, expression of drug transporter gene and epithelial cell phenotype marker, hepatocyte nuclear factor 4 alpha (HNF4a). We also demonstrated that hepatocytes cultured on NAFLD‐like stiffness showed an induction of lipogenic genes along with lowered‐oxidation genes expression, mitochondrial respiration, and glycolytic capacity, 2) increased ROS production, and 3) disruption of the mitochondrial fusion process and dynamics. We observed a significant increase in oxidized glutathione (GSSG) and reduced glutathione (GSH) in hepatocytes cultured on NAFLD‐like stiffness compared to healthy liver stiffness. Similar effect was observed in hepatocytes isolated from NAFLD rat models indicating correlation to physiological conditions. These data suggest a plausible mechanism that increased stiffness modulates hepatocyte function causing liver functional failure.ConclusionsTogether, all these data demonstrates the plausible role of stiffness in regulating hepatocytes function and contribute to metabolic dysregulation in NAFLD. Understanding the impact of stiffness on hepatocytes biology will provide significantly more nuanced data to aid drug development for NAFLD.Support or Funding InformationNIH R01AA027189‐01A1; Nebraska Research Initiative; NIH 1P20GM113126Project SummaryFigure 1

Abstract P169: Renal Denervation Attenuates a Catabolic State in Mice Fed High Salt

Introduction: We recently reported that kidneys accumulate urea as an alternative osmolyte in the renal medulla to concentrate sodium into the urine during high salt intake. This urea-driven water conservation process is coupled with the energy-intensive nature of hepatic urea production, which leads to a catabolic state in mice fed high salt. In this study, we examined the effects of renal denervation on the salt-driven catabolic state since previous studies found that the renal sympathetic nervous system regulates urinary sodium excretion and energy metabolism of some organs such as liver and muscle. Methods: Sham-operated (sham) or renal denervated (RDX) male C57/B6J mice were fed on 0.3% NaCl diet with tap water (NS) or 4% NaCl high salt diet + 0.9% NaCl water to drink (HS) for 4 consecutive weeks (ad libitum), followed by 2 weeks of pair-feeding to match energy intake in all groups. We measured daily food intake and body weight, 24 hours urinary sodium excretion, body sodium content, and activity of liver arginase, a urea producing enzyme. Results: NS + sham and HS + sham mice showed similar body weight gain (NS + sham: +3.6 ± 0.2, HS + sham: +3.4 ± 0.2 g) during ad libitum feeding although HS significantly increased food intake (NS + sham: 3.1 ± 0.04, HS + sham: 3.3 ± 0.04 g/day). After the pair-feeding, HS mice significantly decreased their body weight (NS + sham: +0.9 ± 0.07, HS + sham: -0.6 ± 0.05 g) and increased liver arginase activity (NS + sham: 3792 ± 322, HS + sham: 5412 ± 499 units/L/tissue), confirming the high salt-induced catabolic hepatic urea production. On the other hand, HS did not increase food intake (NS + RDX: 3.2 ± 0.1, HS + RDX: 3.1 ± 0.01 g/day) and liver arginase activity (NS + RDX: 3599 ± 316, HS + RDX: 3363 ± 369 units/L/tissue) in RDX group. In addition, HS + RDX mice did not show pair feeding-induced body weight loss (NS + RDX: +0.6 ± 0.3, HS + RDX: +0.3 ± 0.3 g). HS + RDX mice did not alter 24 hours urinary sodium excretion (HS + sham: 135 ± 6.3, HS + RDX: 142 ± 13 mmol/d/kg) and body sodium content (HS + sham: 0.15 ± 0.003, HS + RDX: 0.15 ± 0.006 mmol/d/kg) compared with HS + sham mice. Conclusion: These findings suggest that renal denervation attenuates the HS-induced body weight loss and catabolic urea production independently of urinary sodium excretion.

A potent liver-mediated mechanism for loss of muscle mass during androgen deprivation therapy.

ContextAndrogen deprivation therapy (ADT) in prostate cancer results in muscular atrophy, due to loss of the anabolic actions of testosterone. Recently, we discovered that testosterone acts on the hepatic urea cycle to reduce amino acid nitrogen elimination. We now hypothesize that ADT enhances protein oxidative losses by increasing hepatic urea production, resulting in muscle catabolism. We also investigated whether progressive resistance training (PRT) can offset ADT-induced changes in protein metabolism.ObjectiveTo investigate the effect of ADT on whole-body protein metabolism and hepatic urea production with and without a home-based PRT program.DesignA randomized controlled trial.Patients and interventionTwenty-four prostate cancer patients were studied before and after 6 weeks of ADT. Patients were randomized into either usual care (UC) (n = 11) or PRT (n = 13) starting immediately after ADT.Main outcome measuresThe rate of hepatic urea production was measured by the urea turnover technique using 15N2-urea. Whole-body leucine turnover was measured, and leucine rate of appearance (LRa), an index of protein breakdown and leucine oxidation (Lox), a measure of irreversible protein loss, was calculated.ResultsADT resulted in a significant mean increase in hepatic urea production (from 427.6 ± 18.8 to 486.5 ± 21.3; P < 0.01) regardless of the exercise intervention. Net protein loss, as measured by Lox/Lra, increased by 12.6 ± 4.9% (P < 0.05). PRT preserved lean body mass without affecting hepatic urea production.ConclusionAs early as 6 weeks after initiation of ADT, the suppression of testosterone increases protein loss through elevated hepatic urea production. Short-term PRT was unable to offset changes in protein metabolism during a state of profound testosterone deficiency.

Abstract P220: High Salt Intake Induces Catabolism Accompanied by Hepatic Urea Osmolyte Production and Decreases Renal Sympathetic Nerve Activity

Introduction: We have recently reported that high salt intake induces the energy-intensive nature of hepatic urea osmolyte production that accompanied the decrease in heart rate (HR). These findings suggest that high salt intake decreases sympathetic nerve activity to reduce cardiovascular energy expenditure for the hepatic urea production. Therefore, we examined the effects of high salt intake on renal sympathetic nerve activity (RSNA) by using a radiotelemetry system in rats. Methods: We inserted the radiotelemetry system into male Sprague Dawley (SD) rats for recording RSNA and HR. After 2 weeks recovery, we fed the rats 0.3% NaCl diet (NS) with tap water to drink (NS + tap), 4% NaCl diet with tap water (HS + tap), and 4% NaCl diet with saline (HS + saline) for 4 days in this order, and kept monitoring their HR and RSNA. In the separate experiment, we also fed male SD rats NS + tap or HS + saline for 6 consecutive weeks to confirm a catabolic state in HS + saline rats. Results: Rats exhibited marked reductions in RSNA and HR during HS + saline phase compared with other phases. HS + saline rats significantly decreased body weight (369±35 g) compared with NS + tap rats (405±48 g) despite of the similar daily food intake (18.5±1.3 vs. 19.2±1.6 g/day). And HS + saline rats increased liver arginase, a urea producing enzyme, activity (1561±121 units/L/mg) compared with NS + tap rats (1337±131 units/L/mg) at 6 weeks after the feeding. Conclusion: High salt intake decreased RSNA accompanied by the catabolic urea production in rats. These findings suggest that the sympathetic nervous system is one of the key regulators to reduce cardiovascular energy expenditure, which could support the energy-intensive nature of hepatic urea production in high salt-fed rats.

Inhibition of the RhoGTPase Cdc42 by ML141 enhances hepatocyte differentiation from human adipose-derived mesenchymal stem cells via the Wnt5a/PI3K/miR-122 pathway: impact of the age of the donor

BackgroundHuman adipose-derived mesenchymal stem cells (hADSCs) are promising cells that may promote hepatocyte differentiation (Hep-Dif) and improve liver function, but the involvement of Cdc42, a key small RhoGTPase which plays a crucial role in aging, is still not well established. We hypothesized that the inhibition of Cdc42 may rescue the hepatogenic potential of hADSCs derived from aged donors.MethodshADSCs isolated from 61 women of different ages were cultured for evaluation of the proliferation of cells, adherence, apoptosis, immunomodulation, immunophenotyping, multipotency, gene expression, and cell function during Hep-Dif. Inhibition of Cdc42 by ML141 was realized during two phases: initiation (days –2 to 14 (D–2/14)) from undifferentiated to hepatoblast-like cells, or maturation (days 14 to 28 (D14/28)) from undifferentiated to hepatocyte-like cells. Mechanistic insights of the Wnt(s)/MAPK/PI3K/miR-122 pathways were studied.ResultsCdc42 activity in undifferentiated hADSCs showed an age-dependent significant increase in Cdc42-GTP correlated to a decrease in Cdc42GAP; the low potentials of cell proliferation, doubling, adherence, and immunomodulatory ability (proinflammatory over anti-inflammatory) contrary to the apoptotic index of the aged group were significantly reversed by ML141. Aged donor cells showed a decreased potential for Hep-Dif which was rescued by ML141 treatment, giving rise to mature and functional hepatocyte-like cells as assessed by hepatic gene expression, cytochrome activity, urea and albumin production, low-density lipoprotein (LDL) uptake, and glycogen storage. ML141-induced Hep-Dif showed an improvement in mesenchymal-epithelial transition, a switch from Wtn-3a/β-catenin to Wnt5a signaling, involvement of PI3K/PKB but not the MAPK (ERK/JNK/p38) pathway, induction of miR-122 expression, reinforcing the exosomes release and the production of albumin, and epigenetic changes. Inhibition of PI3K and miR-122 abolished completely the effects of ML141 indicating that inhibition of Cdc42 promotes the Hep-Dif through a Wnt5a/PI3K/miR-122/HNF4α/albumin/E-cadherin-positive action. The ML141(D–2/14) protocol had more pronounced effects when compared with ML141(D14/28); inhibition of DNA methylation in combination with ML141(D–2/14) showed more efficacy in rescuing the Hep-Dif of aged hADSCs. In addition to Hep-Dif, the multipotency of aged hADSC-treated ML141 was observed by rescuing the adipocyte and neural differentiation by inducing PPARγ/FABP4 and NeuN/O4 but inhibiting Pref-1 and GFAP, respectively.ConclusionML141 has the potential to reverse the age-related aberrations in aged stem cells and promotes their hepatogenic differentiation. Selective inhibition of Cdc42 could be a potential target of drug therapy for aging and may give new insights on the improvement of Hep-Dif.

Testosterone prevents protein loss via the hepatic urea cycle in human.

The urea cycle is a rate-limiting step for amino acid nitrogen elimination. The rate of urea synthesis is a true indicator of whole-body protein catabolism. Testosterone reduces protein and nitrogen loss. The effect of testosterone on hepatic urea synthesis in humans has not been studied. To determine whether testosterone reduces hepatic urea production. An open-label study. Eight hypogonadal men were studied at baseline, and after two weeks of transdermal testosterone replacement (Testogel, 100 mg/day). The rate of hepatic urea synthesis was measured by the urea turnover technique using stable isotope methodology, with 15N2-urea as tracer. Whole-body leucine turnover was measured, from which leucine rate of appearance (LRa), an index of protein breakdown and leucine oxidation (Lox), a measure of irreversible protein loss, were calculated. Testosterone administration significantly reduced the rate of hepatic urea production (from 544.4 ± 71.8 to 431.7 ± 68.3 µmol/min; P < 0.01), which was paralleled by a significant reduction in serum urea concentration. Testosterone treatment significantly reduced net protein loss, as measured by percent Lox/LRa, by 19.3 ± 5.8% (P < 0.05). There was a positive association between Lox and hepatic urea production at baseline (r2 = 0.60, P < 0.05) and after testosterone administration (r2 = 0.59, P < 0.05). Testosterone replacement reduces protein loss and hepatic urea synthesis. We conclude that testosterone regulates whole-body protein metabolism by suppressing the urea cycle.

Combretum lanceolatum flowers ethanol extract inhibits hepatic gluconeogenesis: an in vivo mechanism study

Context Ethnopharmacological studies have demonstrated that plants of the Combretum genus presented antidiabetic activity, including Combretum lanceolatum Pohl ex Eichler (Combretaceae).Objective This study investigated the hepatic mechanisms of action of C. lanceolatum flowers ethanol extract (ClEtOH) related to its antihyperglycaemic effect in streptozotocin-diabetic rats.Materials and methods Male Wistar rats were divided into normal (N) and diabetic control (DC) rats treated with vehicle (water); diabetic rats treated with 500 mg/kg metformin (DMet) or 500 mg/kg ClEtOH (DT500). After 21 d of treatment, hepatic glucose and urea production were investigated through in situ perfused liver with l-glutamine. Changes in the phosphoenolpyruvate carboxykinase (PEPCK) levels and in the activation of adenosine monophosphate-activated protein kinase (AMPK) and insulin-signalling intermediates were also investigated.Results Similar to DMet, DT500 rats showed a reduction in the rates of hepatic production of glucose (46%) and urea (22%) in comparison with DC. This reduction was accompanied by a reduction in the PEPCK levels in liver of DT500 (28%) and DMet (43%) when compared with DC. AMPK phosphorylation levels were higher in the liver of DT500 (17%) and DMet (16%) rats. The basal AKT phosphorylation levels were increased in liver of DT500 rats, without differences in the insulin-stimulated AKT phosphorylation and in the insulin receptor levels between DC and DT500 rats.Discussion and conclusion The antidiabetic activity of ClEtOH can be attributed, at least in part, to inhibition of hepatic gluconeogenesis, probably due to the activation of both AMPK and AKT effectors and reduction in the PEPCK levels.

Cost-effective differentiation of hepatocyte-like cells from human pluripotent stem cells using small molecules

Significant efforts have been invested into the differentiation of stem cells into functional hepatocyte-like cells that can be used for cell therapy, disease modeling and drug screening. Most of these efforts have been concentrated on the use of growth factors to recapitulate developmental signals under in vitro conditions. Using small molecules instead of growth factors would provide an attractive alternative since small molecules are cell-permeable and cheaper than growth factors. We have developed a protocol for the differentiation of human embryonic stem cells into hepatocyte-like cells using a predominantly small molecule–based approach (SM-Hep). This 3 step differentiation strategy involves the use of optimized concentrations of LY294002 and bromo-indirubin-3’-oxime (BIO) for the generation of definitive endoderm; sodium butyrate and dimethyl sulfoxide (DMSO) for the generation of hepatoblasts and SB431542 for differentiation into hepatocyte-like cells. Activin A is the only growth factor required in this protocol. Our results showed that SM-Hep were morphologically and functionally similar or better compared to the hepatocytes derived from the growth-factor induced differentiation (GF-Hep) in terms of expression of hepatic markers, urea and albumin production and cytochrome P450 (CYP1A2 and CYP3A4) activities. Cell viability assays following treatment with paradigm hepatotoxicants Acetaminophen, Chlorpromazine, Diclofenac, Digoxin, Quinidine and Troglitazone showed that their sensitivity to these drugs was similar to human primary hepatocytes (PHHs). Using SM-Hep would result in 67% and 81% cost reduction compared to GF-Hep and PHHs respectively. Therefore, SM-Hep can serve as a robust and cost effective replacement for PHHs for drug screening and development.

Perfusion flow rate substantially contributes to the performance of the HepaRG‐AMC‐bioartificial liver

Bioartificial livers (BALs) are bioreactors containing liver cells that provide extracorporeal liver support to liver-failure patients. Theoretically, the plasma perfusion flow rate through a BAL is an important determinant of its functionality. Low flow rates can limit functionality due to limited substrate availability, and high flow rates can induce cell damage. This hypothesis was tested by perfusing the AMC-BAL loaded with the liver cell line HepaRG at four different medium flow rates (0.3, 1.5, 5, and 10 mL/min). Hepatic functions ammonia elimination, urea production, lactate consumption, and 6β-hydroxylation of testosterone showed 2-20-fold higher rates at 5 mL/min compared to 0.3 mL/min, while cell damage remained stable. However, at 10 mL/min cell damage was twofold higher, and maximal hepatic functionality was not changed, except for an increase in lactate elimination. On the other hand, only a low flow rate of 0.3 mL/min allowed for an accurate measurement of the ammonia and lactate mass balance across the bioreactor, which is useful for monitoring the BAL's condition during treatment. These results show that (1) the functionality of a BAL highly depends on the perfusion rate; (2) there is a universal optimal flow rate based on various function and cell damage parameters (5 mL/min for HepaRG-BAL); and (3) in the current set-up the mass balance of substrate, metabolite, or cell damage markers between in-and out-flow of the bioreactor can only be determined at a suboptimal, low, perfusion rate (0.3 mL/min for HepaRG-BAL).

Hypoglycemic effect of the hydroalcoholic extract of leaves of Averrhoa carambola L. (Oxalidaceae)

The effect of the oral treatment (20 mg/kg x day) with the hydroalcoholic extract of leaves of Averrhoa carambola L. (HELAC) on fasting glycemia (15 h) was examined. For this purpose, rats that received vehicle (Control group) or HELAC (HELAC group) during 15 days were compared. HELAC group showed lower fasting glycemia (p<0.05). In contrast, livers from HELAC group showed higher (p<0.05) glucose production from L-alanine (5 mM). This effect was mediated, at least part of it, by an activation of the catabolism of L-alanine inferred by the increased hepatic urea (p<0.05) and L-lactate (p<0.05) production. Differently of L-alanine, the glucose production from L-glutamine (5 mM), L-lactate (2 mM) and glycerol (2 mM) was similar (Control group vs. HELAC group). In addition, the HELAC treatment did not change the glucose uptake in soleus muscles, inferred by the incorporation of [14C]-glucose to glycogen (glycogen synthesis) and [14C]-lactate production. Thus, we can conclude that the reduction of fasting glycemia promoted by the treatment with HELAC was not mediated by an inhibition of hepatic gluconeogenesis and/or an increased glucose uptake by muscles.

Urea and short-chain fatty acids metabolism in Holstein cows fed a low-nitrogen grass-based diet

Three ruminally cannulated and multicatheterised lactating dairy cows were used to investigate the effect of different supplement strategies to fresh clover grass on urea and short-chain fatty acid (SCFA) metabolism in a zero-grazing experiment with 24-h blood and ruminal samplings. Fresh clover grass was cut every morning and offered from 0800 to 1500 h. Maize silage was fed at 1530 h. The three treatments, arranged in a Latin square, differed by timing of feeding rolled barley and soya-bean hulls relative to fresh clover grass. All diets had the same overall composition. Treatments were soya-bean hulls fed at 0700 h and barley fed at 1530 h (SAM), barley fed at 0700 h and soya-bean hulls fed at 1530 h (BAM), and both soya-bean hulls and barley fed at 1530 h (SBPM). The grass had an unexpectedly low content of crude protein (12.7%) and the cows were severely undersupplied with rumen degradable protein. The treatment effects were numerically small; greater arterial ammonia concentration, net portal flux of ammonia and net hepatic flux of urea during part of the day were observed when no supplementary carbohydrate was fed before grass feeding. A marked diurnal variation in ruminal fermentation was observed and grass feeding increased ruminal concentrations of propionate and butyrate. The net portal fluxes of propionate, butyrate, isovalerate and valerate as well as the net hepatic uptake of propionate, butyrate, valerate and caproate increased after feeding at 0700 h. The hepatic extraction of butyrate showed a relatively large depression with grass feeding with nadir at 1200 to 1330 h. The increased net portal absorption and the decreased hepatic extraction resulted in an approximately six-fold increase in the arterial blood concentration of butyrate. The gut entry rate of urea accounted for 70 ± 10% of the net hepatic production of urea. Saliva contributed to 14% of the total amount of urea recycled to the gut. Urea recycling to the gut was equivalent to 58% of the dietary nitrogen intake. Despite the severe undersupply of rumen degradable protein, the portal-drained viscera did not extract more than 4.3% of the urea supplied with arterial blood. This value is in line with the literature values for cows fed diets only moderately deficient in rumen degradable protein and indicates that cows maximise urea transfer across gut epithelia even when the diet is moderately deficient in rumen degradable protein.

Glycemia recovery with oral amino acid administration during experimental short-term insulin-induced hypoglycemia

Aim The acute effects of the oral administration of l-alanine ( l-ala), l-glutamine ( l-gln), l-ala+ l-gln, and l-alanyl- l-glutamine (AGP) on glycemia recovery during short-term insulin-induced hypoglycemia (IIH) were compared. Methods For this purpose, the blood glucose levels of 24-h-fasted rats that received intraperitoneal injections of regular insulin (IIH group) or saline [control (COG) group] and, 15 min later, oral administration of l-ala (100 mg/kg), l-gln (100 mg/kg), l-ala (50 mg/kg)+ l-gln (50 mg/kg), or AGP (100 mg/kg) were compared. Liver perfusion experiments and blood collection to measure blood glucose levels were performed 30 min after insulin (1.0 U/kg) or saline injection. Livers from the IIH and COG groups were perfused with saturating concentrations of l-ala, l-gln, l-ala+ l-gln, or AGP, and the maximal hepatic production of glucose, urea, ammonia, l-lactate, and pyruvate was evaluated. Results In contrast with l-gln, l-ala+ l-gln, or AGP, the oral administration of l-ala promoted glycemia recovery. In agreement with these results, livers from IIH rats showed maximal hepatic production of glucose and urea from l-ala with 50% of the amount used to obtain the maximal hepatic production of glucose and urea in livers from COG rats. In contrast with l-gln, l-ala+ l-gln, or AGP, the maximal hepatic production of urea from l-ala occurred in the absence of ammonia accumulation. Conclusion The results indicate that the best glycemia recovery promoted by the oral administration of l-ala was a consequence of the higher efficiency of the livers from IIH rats in producing glucose from l-ala.

Osmoregulation in elasmobranch fish — A review

In recent years our understanding of the control of ion and urea metabolism in elasmobranch fish has increased with many more species being investigated. This has demonstrated that some species regarded previously as stenohaline marine are, at least partially, euryhaline and may survive in environments less concentrated than full seawater. In elasmobranch fish the success of the osmotic strategy depends on retaining large concentrations of plasma urea in addition to relatively high, in comparison to most other vertebrates, plasma concentrations of sodium and chloride. The strategy therefore depends on the integrated control of hepatic urea production and branchial and renal urea excretion and also on a balance of salt input at the gills and gut with salt output at the gills, kidney and via the unique elasmobranch rectal gland. This integrated response is, at least in part, controlled by a series of osmoregulatory hormones and their possible role in the control of osmoregulatory organs will be discussed. In this presentation recent findings will be reviewed and the osmoregulatory strategies of a partially euryhaline species, Scyliorhinus canicula, with a fully euryhaline migratory species, Carcharhinus leucas, will be compared. This will allow new models for the control of ion and urea metabolism in elasmobranchs to be proposed for future research.

Hepatic urea biosynthesis in the euryhaline elasmobranchCarcharhinus leucas

Plasma urea levels and hepatic urea production in the euryhaline bull shark, Carcharhinus leucas, acclimated to freshwater and seawater environments were measured. It was found that plasma urea concentration increased with salinity and that this increase was, in part, the result of a significant increase in hepatic production of urea. This study provides direct evidence that hepatic production of urea plays an important role in the osmoregulatory strategy of C. leucas.

Comparative acute effects of leptin and insulin on gluconeogenesis and ketogenesis in perfused rat liver

The acute effects of physiological levels of leptin (10 ng ml(-1)) and insulin (20 microU ml(-1)) on hepatic gluconeogenesis and ketogenesis were compared. Leptin or insulin alone decreased (p<0.05) the activation of hepatic glucose, L-lactate and urea production from L-alanine. However, the hepatic glucose production was not modified if leptin was combined with insulin. These results indicated that both, i.e. leptin and insulin, could promote a non-additive reduction in the rate of catabolism of L-alanine. However, in contrast with insulin (p<0.05), leptin did not inhibit the activation of hepatic glucose production from pyruvate or glycerol. On the other hand, activation of hepatic production of acetoacetate and beta-hydroxybutyrate from octanoate was not affected by leptin or insulin. Thus, our data demonstrate that the acute effect of leptin on hepatic metabolism was partially similar to insulin (activation of glucose production from L-alanine and activation of acetoacetate or beta-hydroxybutyrate production from octanoate) and partially different from insulin (activation of glucose production from pyruvate or glycerol).

Fulminant hepatic failure

Abstract Analysis of the first 150 cases collected from 73 centers reporting to the Fulminant Hepatic Failure Surveillance Study showed that 80 patients had presumable viral hepatitis, of whom 62 died. Of 41 patients who had recent surgery, 36 died. In 35 patients massive liver necrosis developed less than three weeks after halothane anesthesia, and 27 (77 per cent) of these had multiple exposures to halothane. The risk from halothane is small, but this complication was present in nearly one quarter of the cases reported in our study. When the use of halothane is desired, multiple exposure should be avoided, if possible. Moreover, postoperative fever after exposure to halothane, otherwise "unexplained," is an important warning sign, and should be thoroughly investigated and taken into consideration when further exposure to this anesthetic is contemplated. The physician prescribing halothane must balance need against risk.

Role of Quercetin on Hepatic Urea Production in Acute Renal Failure

Acute renal failure (ARF) is a serious damage of renal function induced by various nephrotoxic drugs, ischemia, bilateral urethral obstruction, trauma and unilateral nephrectomy. Dramatic clinical syndrome, azotemia, develops as a result of hypovolemia, oliguria, reduced glomerular filtration and acidosis. In addition to classic medications recent studies give more attention to beneficial effect of natural plant products as bioflavonoids. We have studied the influence of bioflavonoid, quercetin, on hepatic urea production in glycerol induced ARF in the rats. Male Sprague Dawley rats were used in the experiment. The value of urea production in the liver was determined by measuring of liver arginase activity, the terminal enzyme of urea cycle. Arginase activity was increased (p<0.01) as well as urea level (p<0.001) 48 h after glycerol administration. Pretreatment by quercetin suppressed the arginase activity in the liver (p<0.05) and plasma levels of urea (p<0.01). So, we have concluded that quercetin may be beneficial in glycerol induced ARF.

Influence of N-acetylcysteine on hepatic amino acid metabolism in patients undergoing orthotopic liver transplantation

Experimental treatment with the antioxidant and glutathione precursor N-acetylcysteine (NAC) has been performed in orthotopic liver transplantation (OLT) to reduce reperfusion injury. To investigate the effect of NAC on the hepatic and intestinal amino acid metabolism, intraoperative amino acid exchange rates were studied in liver transplant recipients with high dose NAC treatment (n = 10) and in control patients (n = 9). Treatment with NAC was found to cause a loss of amino acids and increased urea nitrogen release from the liver graft. The net balance of most amino acids was shifted to increased hepatic release or decreased hepatic uptake. The initial cumulative splanchnic release of all proteinogenic amino acids in the NAC treated group was significantly higher than in the control group. These findings are tentatively explained by an increased net protein catabolism in the liver. The increased hepatic urea and glutamine production rate of the NAC treated patients is expected to increase the energy and oxygen demand of the liver in this critical situation. Thus, NAC may have caused marked metabolic disturbances in the freshly implanted graft. The dosage of NAC should therefore be modified to avoid these disadvantages.

Hepatic Hemodynamics and Cell Functions in Human and Experimental Sepsis

Hepatic Hemodynamics and Cell Functions in Human and Experimental Sepsis