Glycogen levels and glycogen catabolism in livers from arthritic rats

Effects of resveratrol on rheumatic symptoms and hepatic metabolism of arthritic rats

OBJECTIVES

Resveratrol has been studied as a potential agent for treating rheumatic conditions; however, this compound suppresses glucose synthesis and glycogen catabolism when infused in perfused livers of both arthritic and healthy rats. This study investigated the effects of oral administration of resveratrol on inflammation and liver metabolism in rats with arthritis induced by Freund's adjuvant, which serves as rheumatoid arthritis model.

METHODS

Holtzman rats, both healthy and exhibiting arthritic symptoms, were orally treated with resveratrol at doses varying from 25 to 500 mg/kg for a 5-day period preceding arthritis induction, followed by an additional 20-day period thereafter. Paw edema, arthritic score and hepatic myeloperoxidase activity were assessed to evaluate inflammation. Glycogen catabolism and gluconeogenesis from lactate were respectively evaluated in perfused livers from fed and fasted rats.

RESULTS

Resveratrol decreased the liver myeloperoxidase activity at doses above 100 mg/kg, and decreased the paw edema and delayed the arthritic score at doses above 250 mg/kg. The hepatic gluconeogenesis was decreased in arthritic rats and resveratrol did not improve it. However, resveratrol did not negatively modify the gluconeogenesis in livers of healthy and arthritic rats. Glycogen catabolism was in part and slightly modified by resveratrol in the liver of arthritic and healthy rats.

CONCLUSIONS

It is improbable that resveratrol negatively affects the liver metabolism, especially considering that gluconeogenesis is highly fragile to changes in cellular architecture. The findings suggest that resveratrol could serve as alternative for treating rheumatoid arthritis. Nevertheless, prudence is advised regarding its transient effects on liver metabolism.

Resveratrol biotransformation and actions on the liver metabolism of healthy and arthritic rats

AIMS

To investigate the effects of resveratrol on glycogen catabolism and gluconeogenesis in perfused livers of healthy and arthritic rats. The actions of resveratrol-3-O-glucuronide (R3G) and the biotransformation of resveratrol into R3G was further evaluated in the livers.

MAIN METHODS

arthritis was induced with Freund's adjuvant. Resveratrol at concentrations of 10, 25, 50, 100 and 200 μM and 200 μM R3G were introduced in perfused livers. Resveratrol and metabolites were measured in the outflowing perfusate. Respiration of isolated mitochondria and activity of gluconeogenic enzymes were also evaluated in the livers.

KEY FINDINGS

resveratrol inhibited glycogen catabolism when infused at concentrations above 50 μM and gluconeogenesis even at 10 μM in both healthy and arthritic rat livers, but more sensitive in these latter. Resveratrol above 100 μM inhibited ADP-stimulated respiration and the activities of NADH- and succinate-oxidases in mitochondria, which were partially responsible for gluconeogenesis inhibition. Pyruvate carboxylase activity was inhibited by 25 μM resveratrol and should inhibit gluconeogenesis already at low concentrations. Resveratrol was significantly metabolized to R3G in healthy rat livers, however, R3G formation was lower in arthritic rat livers. The latter must be in part a consequence of a lower glucose disposal for glucuronidation. When compared to resveratrol, R3G inhibited gluconeogenesis in a lower extension and glycogen catabolism in a higher extension.

SIGNIFICANCE

the effects of resveratrol and R3G tended to be transitory and existed only when the resveratrol is present in the organ, however, they should be considered because significant serum concentrations of both are found after oral ingestion of resveratrol.

Kinetic mechanisms by which nickel alters the calcium (Ca2+) transport in intact rat liver

In the present work, the multiple-indicator dilution (MID) technique was used to investigate the kinetic mechanisms by which nickel (Ni²⁺) affects the calcium (Ca²⁺) transport in intact rat liver. ⁴⁵Ca²⁺ and extra- and intracellular space indicators were injected in livers perfused with 1 mM Ni²⁺, and the outflow profiles were analyzed by a mathematical model. For comparative purposes, the effects of norepinephrine were measured. The influence of Ni²⁺ on the cytosolic Ca²⁺ concentration ([Ca²⁺]_c) in human hepatoma Huh7 cells and on liver glycogen catabolism, a biological response sensitive to cellular Ca²⁺, was also evaluated. The estimated transfer coefficients of ⁴⁵Ca²⁺ transport indicated two mechanisms by which Ni²⁺ increases the [Ca²⁺]_c in liver under steady-state conditions: (1) an increase in the net efflux of Ca²⁺ from intracellular Ca²⁺ stores due to a stimulus of Ca²⁺ efflux to the cytosolic space along with a diminution of Ca²⁺ re-entry into the cellular Ca²⁺ stores; (2) a decrease in Ca²⁺ efflux from the cytosolic space to vascular space, minimizing Ca²⁺ loss. Glycogen catabolism activated by Ni²⁺ was transient contrasting with the sustained activation induced by norepinephrine. Ni²⁺ caused a partial reduction in the norepinephrine-induced stimulation in the [Ca²⁺]_c in Huh7 cells. Our data revealed that the kinetic parameters of Ca²⁺ transport modified by Ni²⁺ in intact liver are similar to those modified by norepinephrine in its first minutes of action, but the membrane receptors or Ca²⁺ transporters affected by Ni²⁺ seem to be distinct from those known to be modulated by norepinephrine.

Metabonomic-Transcriptome Integration Analysis on Osteoarthritis and Rheumatoid Arthritis

Purpose

This study is aimed at exploring the potential metabolite/gene biomarkers, as well as the differences between the molecular mechanisms, of osteoarthritis (OA) and rheumatoid arthritis (RA).

Methods

Transcriptome dataset GSE100786 was downloaded to explore the differentially expressed genes (DEGs) between OA samples and RA samples. Meanwhile, metabolomic dataset MTBLS564 was downloaded and preprocessed to obtain metabolites. Then, the principal component analysis (PCA) and linear models were used to reveal DEG-metabolite relations. Finally, metabolic pathway enrichment analysis was performed to investigate the differences between the molecular mechanisms of OA and RA.

Results

A total of 976 DEGs and 171 metabolites were explored between OA samples and RA samples. The PCA and linear module analysis investigated 186 DEG-metabolite interactions including Glycogenin 1- (GYG1-) asparagine_54, hedgehog acyltransferase- (HHAT-) glucose_70, and TNF receptor-associated factor 3- (TRAF3-) acetoacetate_35. Finally, the KEGG pathway analysis showed that these metabolites were mainly enriched in pathways like gap junction, phagosome, NF-kappa B, and IL-17 pathway.

Conclusions

Genes such as HHAT, GYG1, and TRAF3, as well as metabolites including glucose, asparagine, and acetoacetate, might be implicated in the pathogenesis of OA and RA. Metabolites like ethanol and tyrosine might participate differentially in OA and RA progression via the gap junction pathway and phagosome pathway, respectively. TRAF3-acetoacetate interaction may be involved in regulating inflammation in OA and RA by the NF-kappa B and IL-17 pathway.

Fatty acids uptake and oxidation are increased in the liver of rats with adjuvant-induced arthritis

Severe rheumatoid cachexia is associated with pronounced loss of muscle and fat mass in patients with advanced rheumatoid arthritis. This condition is associated with dyslipidemia and predisposition to cardiovascular diseases. Circulating levels of triglycerides (TG) and free fatty acids (FFA) have not yet been consistently defined in severe arthritis. Similarly, the metabolism of these lipids in the arthritic liver has not yet been clarified. Aiming at filling these gaps this study presents a characterization of the circulating lipid profile and of the fatty acids uptake and metabolism in perfused livers of rats with adjuvant-induced arthritis. The levels of TG and total cholesterol were reduced in both serum (10-20%) and liver (20-35%) of arthritic rats. The levels of circulating FFA were 40% higher in arthritic rats, possibly in consequence of cytokine-induced adipose tissue lipolysis. Hepatic uptake and oxidation of palmitic and oleic acids was higher in arthritic livers. The phenomenon results possibly from a more oxidized state of the arthritic liver. Indeed, NADPH/NADP⁺ and NADH/NAD⁺ ratios were 30% lower in arthritic livers, which additionally presented higher activities of the citric acid cycle driven by both endogenous and exogenous FFA. The lower levels of circulating and hepatic TG possibly are caused by an increased oxidation associated to a reduced synthesis of fatty acids in arthritic livers. These results reveal that the lipid hepatic metabolism in arthritic rats presents a strong catabolic tendency, a condition that should contribute to the marked cachexia described for arthritic rats and possibly for the severe rheumatoid arthritis.

Sacrificial layer technique for axial force post assay of immature cardiomyocytes

Immature primary and stem cell-derived cardiomyocytes provide useful models for fundamental studies of heart development and cardiac disease, and offer potential for patient specific drug testing and differentiation protocols aimed at cardiac grafts. To assess their potential for augmenting heart function, and to gain insight into cardiac growth and disease, tissue engineers must quantify the contractile forces of these single cells. Currently, axial contractile forces of isolated adult heart cells can only be measured by two-point methods such as carbon fiber techniques, which cannot be applied to neonatal and stem cell-derived heart cells because they are more difficult to handle and lack a persistent shape. Here we present a novel axial technique for measuring the contractile forces of isolated immature cardiomyocytes. We overcome cell manipulation and patterning challenges by using a thermoresponsive sacrificial support layer in conjunction with arrays of widely separated elastomeric microposts. Our approach has the potential to be high-throughput, is functionally analogous to current gold-standard axial force assays for adult heart cells, and prescribes elongated cell shapes without protein patterning. Finally, we calibrate these force posts with piezoresistive cantilevers to dramatically reduce measurement error typical for soft polymer-based force assays. We report quantitative measurements of peak contractile forces up to 146 nN with post stiffness standard error (26 nN) far better than that based on geometry and stiffness estimates alone. The addition of sacrificial layers to future 2D and 3D cell culture platforms will enable improved cell placement and the complex suspension of cells across 3D constructs.

Profiling of dihydroorotate dehydrogenase, p38 and JAK inhibitors in the rat adjuvant-induced arthritis model: a translational study

BACKGROUND AND PURPOSE

Translational animal models are essential in the prediction of the efficacy and side effects of new chemical entities. We have carried out a thorough study of three distinct disease-modifying antirheumatic drugs (DMARDs) in an adjuvant-induced arthritis (AIA) model in the rat and critically appraised the results in the context of the reported clinical experience in rheumatoid arthritis (RA) patients.

EXPERIMENTAL APPROACH

Teriflunomide - a dihydroorotate dehydrogenase (DHODH) inhibitor; AL8697 - a selective p38 MAPK inhibitor; and tofacitinib - a Janus kinase (JAK) inhibitor; were selected as representatives of their class and dose-response studies carried out using a therapeutic 10-day administration scheme in arthritic rats. Paw swelling and body weight were periodically monitored, and joint radiology and histology, lymph organ weight and haematological and biochemical parameters evaluated at study completion.

KEY RESULTS

All three drugs demonstrated beneficial effects on paw swelling, bone lesions and splenomegalia, with p38 inhibition providing the best anti-inflammatory effect and JAK inhibition the best DMARD effect. Leukopenia, body weight loss and gastrointestinal toxicity were dose-dependently observed with teriflunomide treatment. p38 MAPK inhibition induced leukocytosis and increased total plasma cholesterol. JAK inhibition, normalized platelet, reticulocyte and neutrophil counts, and alanine aminotransferase (ALT) levels while inducing lymphopenia and cholesterolemia.

CONCLUSIONS AND IMPLICATIONS

This multiparametric approach can reveal specific drug properties and provide translational information. Whereas the complex profile for p38 inhibition in AIA is not observed in human RA, immunosuppressants such as DHODH and JAK inhibitors show DMARD properties and side effects seen in both AIA and RA.

Protective effects of indomethacin and cyclophosphamide but not of infliximab on liver metabolic changes caused by adjuvant-induced arthritis

In the study, indomethacin, cyclophosphamide, and infliximab were administered to adjuvant-induced arthritic rats to determine if they were able to prevent the abnormalities caused by arthritis on hepatic metabolism. The drugs were administered to arthritic rats, and at the clinical onset of arthritis (day 14 after adjuvant injection), the livers were perfused to evaluate gluconeogenesis, ureagenesis, oxygen uptake, L: -lactate, pyruvate, and ammonia release from L: -alanine. The effects of the drugs on body weight gain and the signs of arthritis (paw edema, appearance of secondary lesions, and weights of lymphoid tissues) were also evaluated. Cyclophosphamide could completely prevent liver metabolic changes and the inflammatory response. Indomethacin restored ureagenesis, minimized the decrease in gluconeogenesis, and exerted a partially beneficial effect on inflammatory reactions. Infliximab did not improve arthritis-induced liver metabolic alterations or inflammatory responses. These results suggest the participation of prostaglandins, but not TNF-α, on arthritis-induced liver metabolic alterations.

Decreased response to cAMP in the glucose and glycogen catabolism in perfused livers of Walker-256 tumor-bearing rats

The hepatic response to cyclic adenosine monophosphate (cAMP) and N6-monobutyryl-cAMP (N6-MB-cAMP) in the glucose and glycogen catabolism and hepatic glycogen levels were evaluated in Walker-256 tumor-bearing rats, on days 5 (WK5), 8 (WK8), and 11 (WK11) after the implantation of tumor. Rats without tumor fed ad libitum (fed control rats) or that received the same daily amount of food ingested by anorexics tumor-bearing rats (pair-fed control rats) or 24 h fasted (fasted control rats) were used as controls. Glucose and glycogen catabolism were measured in perfused liver. Hepatic glycogen levels were lower (p < 0.05) in WK5, WK8, and WK11 rats in comparison with fed control rats, but not in relation to the pair-fed control rats. However, the stimulatory effect of cAMP (3 and 9 μM) in the glycogen catabolism was lower (p < 0.05), respectively, in WK5 and WK8 rats compared to the pair-fed and fed control rats. Accordingly, the suppressive effect of cAMP (6 μM) in the glucose catabolism, under condition of depletion of hepatic glycogen (24 h fast), was lower (p < 0.05) in WK5 and WK11 rats than in fasted control rats. Similarly, the suppressive effect of N6-MB-cAMP (1 μM), a synthetic analogue of cAMP that it is not degraded by phosphodiesterase 3B (PDE3B), in the glucose catabolism was lower (p < 0.05) in WK5 rats compared to fasted control rats. In conclusion, livers of Walker-256 tumor-bearing rats showed lower response to cAMP in the glucose and glycogen catabolism in various stages of tumor development (days 5, 8 and 11), which was probably not due to the lower hepatic glycogen levels nor due to the increased activity of PDE3B.

Effects of simvastatin, atorvastatin, ezetimibe, and ezetimibe + simvastatin combination on the inflammatory process and on the liver metabolic changes of arthritic rats

In this study, simvastatin, atorvastatin, ezetimibe, and ezetimibe + simvastatin combination were administered to arthritic rats, first to determine their effects on the inflammatory response, employing a low-dose adjuvant-induced arthritis model in rats. Arthritis was induced by the subcutaneous injection of a suspension of Mycobacterium tuberculosis (100 μg) in mineral oil [complete Freund's adjuvant used (CFA)] into the plantar surface of the hind paws. Simvastatin(40 mg/kg), atorvastatin(10 mg/kg), ezetimibe(10 mg/kg), ezetimibe(10 mg/kg) + simvastatin(20 mg/kg or 40 mg/kg) were given intragastrically and the treatment began on the day of CFA injection and continued daily up to the 28th day after arthritis induction. The ezetimibe + simvastatin combination was more effective in reducing the inflammatory response in arthritic rats than in atorvastatin, simvastatin, or ezetimibe monotherapy. The observed effect seems to be cholesterol-independent as there were no changes in plasma cholesterol levels. In spite of the benefits on joint lesions, treatment with ezetimibe + simvastatin combination caused a marked increment in liver, kidneys, spleen size, and plasma transaminases activities. Therefore, animals treated with the ezetimibe(10 mg/kg) + simvastatin(40 mg/kg) combination were also submitted to liver perfusion experiments. In this regard, ezetimibe + simvastatin did not improve the liver metabolic alterations seen in control arthritic rats, on the contrary, a worsening was observed in liver production of glucose from alanine, as well as in oxygen uptake. All of these metabolic changes appear to be induced by treatment with ezetimibe + simvastatin combination, as the same metabolic effects were observed in normal and treated arthritic animals.

Histological Changes on Liver Glycogen Storage in Mice (Mus musculus) Caused by Unbalanced Diets

Weight-losing diets have appealed to people who want to lose weight in the short-term. They usually apply high-protein (HP) diets (like Atkin’s, Stillman’s, Scarsdale) which they practice for 2 weeks or so. Unfortunately, these people who have rapid weight loss return to their old habits and quickly regain the weight lost. We have shown in previous work that actually these weight losses have been associated with body fluids, protein and glycogen storage. In our study, we examined the effect of unbalanced diet—related to an HP diet- on liver glycogen storage.

For this study 40 Swiss albino mice consisting of two groups were used. The first group (HPSD) was fed with 25% HP for fifteen days and then were fed standard meals for the remaining 15 days; the other group was fed with standard meals throughout. The two groups were fed their respective diets for 30 days. At the end of 15th, 20th, 25th and 30th days 5 from each group were killed with cervical dislocation. The livers were removed perfused and then fixated.

There were major differences in weight between the first and the fifteenth days. We detected remarkable increase in the weight gain of mice in the remaining 15 days. Glycogen storage was significantly reduced in HPSD (15) stained with PAS. In the others 20th, 25th and 30th days abnormally dense glycogen deposits were observed. Vacuoles in the hepatocyte cytoplasm, brownish deposits within hepatocytes, wide sinusoids, macrovesiculler steatosis structures and hydropic degeneration were observed in PAS and H&E stained HPSD group.

As a result for the HPSD group a significant decrement in glycogen storage at the 15th day and also an accumulation of excessive amounts of glycogen deposits in mice liver was observed in the normal feeding phase.

The metabolic changes caused by dexamethasone in the adjuvant-induced arthritic rat

The action of orally administered dexamethasone (0.2 mg kg(-1) day(-1)) on metabolic parameters of adjuvant-induced arthritic rats was investigated. The body weight gain and the progression of the disease were also monitored. Dexamethasone was very effective in suppressing the Freund's adjuvant-induced paw edema and the appearance of secondary lesions. In contrast, the body weight loss of dexamethasone-treated arthritic rats was more accentuated than that of untreated arthritic or normal rats treated with dexamethasone, indicating additive harmful effects. The perfused livers from dexamethasone-treated arthritic rats presented high content of glycogen in both fed and fasted conditions, as indicated by the higher rates of glucose release in the absence of exogenous substrate. The metabolization of exogenous L: -alanine was increased in livers from dexamethasone-treated arthritic rats in comparison with untreated arthritic rats, but there was a diversion of carbon flux from glucose to L: -lactate and pyruvate. Plasmatic levels of insulin and glucose were significantly higher in arthritic rats following dexamethasone administration. Most of these changes were also found in livers from normal rats treated with dexamethasone. The observed changes in L: -alanine metabolism and glycogen synthesis indicate that insulin was the dominant hormone in the regulation of the liver glucose metabolism even in the fasting condition. The prevalence of the metabolic effects of dexamethasone over those ones induced by the arthritis disease suggests that dexamethasone administration was able to suppress the mechanisms implicated in the development of the arthritis-induced hepatic metabolic changes. It seems thus plausible to assume that those factors responsible for the inflammatory responses in the paws and for the secondary lesions may be also implicated in the liver metabolic changes, but not in the body weight loss of arthritic rats.

Anti-Inflammatory Activity ofCleome gynandraL. on Hematological and Cellular Constituents in Adjuvant-Induced Arthritic Rats

Cleome gynandra L. (cat whiskers) has traditionally been used for the treatment of rheumatic and other inflammatory conditions. In this work, the methanolic extract of the leaves of C. gynandra exhibited significant anti-inflammatory activity in adjuvant-induced arthritic rats. Phytochemical screening was carried out to ascertain the qualitative composition of the leaves. Arthritis was induced by Freund's complete adjuvant. A significant decrease in paw edema with a remarkable increase in body weight was observed following oral administration of the leaf extract (150 mg/kg of body weight). The alterations in hematological and other biochemical parameters were restored to near normal after a treatment period of 30 days. These results demonstrate that the plant extract has no harmful effect and exerts in vivo anti-inflammatory properties against adjuvant-induced arthritis.

Metabolic fate of extrahepatic arginine in liver after burn injury

Increased nitrogen loss in the form of urea is a hallmark of the metabolic aberrations that occur after burn injury. As the immediate precursor for urea production is arginine, we have conducted an investigation on the metabolic fate of arginine in the liver to shed light on the metabolic characteristics of this increased nitrogen loss. Livers from 25% total surface burn (n = 8) and sham burn rats (n = 8) were perfused in a recycling fashion with a medium containing amino acids and stable isotope labeled l-[(15) N(2)-guanidino, 5,5-(2)H(2)]arginine for 120 minutes. The rates of glucose and urea production and oxygen consumption were measured. The rate of unidirectional arginine transport and the intrahepatic metabolic fate of arginine in relation to urea cycle activity were quantified by tracing the disappearance rate of the arginine tracer from and the appearance rate of [(15)N(2)]urea in the perfusion medium. Perfused livers from burned rats showed higher rates of total urea production (mean +/- SE, 4.471 +/- 0.274 v 3.235 +/- 0.261 mumol. g dry liver(-1). min(-1); P <.01). This was accompanied by increased hepatic arginine transport (1.269 +/- 0.263 v 0.365 +/- 0.021 mumol. g dry liver(-1). min(-1)) and an increased portion of urea production from the transported extrahepatic arginine (12.9% +/- 2.9% v 3.5% +/- 0.4%, P <.05). The disposal of arginine via nonurea pathways was also increased (0.702 +/- 0.185 v 0.257 +/- 0.025 mumol/g dry weight(-1)/min(-1); P <.05). We propose that increased inward transport and utilization of extrahepatic arginine by the liver contributes to the accelerated urea production after burn injury and accounts, in part, for its conditional essentiality in the nutritional support of burn patients.

Animal models of human disease in drug safety assessment

Animal models of human disease have been widely used in drug discovery, but they are rarely utilized in toxicological research and screening (except for transgenic models in carcinogenicity testing). Although genetic and/or acquired pathophysiological alterations associated with a particular disease may greatly exacerbate toxic responses to drugs in certain patient subsets, these pre-existing pathological conditions are usually not considered in preclinical safety assessment. Examples of disease-related determinants of susceptibility include disruption of the cytokine network in pro-inflammatory conditions, mitochondrial alterations and oxidative stress in certain neurodegenerative diseases, altered antioxidant defense in certain viral infections, and altered gene expression and mitochondrial dysfunction in type 2 diabetes. Hence, if cellular stress caused by drugs or metabolites and the disease-related effects are superimposed, then an individual can become sensitized to potential drug toxicity. Animal models of modest inflammation indeed can potentiate the toxicity of certain drugs. Similarly, rodent models of type 2 diabetes predispose the animals to hepatotoxic effects of thiazolidinediones antidiabetics. In conclusion, it is suggested that tailor-made and simplified models be adopted and increasingly used, in spite of clear limitations, as optimal substrates for satellite toxicity studies to facilitate candidate selection, help predict rare and unexpected toxicity, and identify new biomarkers.

Kinetic properties of the glucose 6-phosphatase of the liver from arthritic rats

According to previous reports, adjuvant-induced arthritic rats present reduced activities of the hepatic glucose 6-phosphatase. A kinetic study was done in order to characterize this phenomenon. Microsomes were isolated from livers of arthritic and control rats (Holtzman strain) and the glucose 6-phosphatase was measured at various temperatures (13-37 degrees C) and glucose 6-phosphate concentrations. Irrespective of the temperature, the enzyme from arthritic rats presented a reduction of both V(max) and K(M). Detergent treatment of liver microsomes from control rats increased the activity, but no increase was found when microsomes from arthritic rats were treated in the same way. The mannose 6-phosphatase activity of detergent-treated microsomes from arthritic rats was only 25% of the activity found with detergent-treated microsomes from control rats. Without detergent treatment, the mannose 6-phosphatase activities of both control and arthritic rats were minimal. The activation energy, derived from V(max), was not changed by arthritis. In vivo arthritic rats presented higher hepatic glucose 6-phosphate concentrations, a phenomenon that is consistent with a reduced activity of glucose 6-phosphatase. It was concluded that in arthritic rats, the hydrolase is probably reduced, without a similar change in the translocase activity.

The urea cycle in the liver of arthritic rats

The urea cycle in the liver of adjuvant-induced arthritic rats was investigated using the isolated perfused liver. Urea production in livers from arthritic rats was decreased during substrate-free perfusion and also in the presence of the following substrates: alanine, alanine + ornithine, ammonia, ammonia + lactate, ammonia + pyruvate and glutamine but increased when arginine and citrulline + aspartate were the substrates. No differences were found with ammonia + aspartate, ammonia + aspartate + glutamate, aspartate, aspartate + glutamate and citrulline. Ammonia consumption was smaller in the arthritic condition when the substance was infused together with lactate or pyruvate but higher when the substance was simultaneously infused with aspartate or aspartate + glutamate. Glucose production tended to correlate with the smaller or higher rates of urea synthesis. Blood urea was higher in arthritic rats (+25.6%), but blood ammonia was lower (-32.2%). Critical for the synthesis of urea from various substrates in arthritic rats seems to be the availability of aspartate, whose production in the liver is probably limited by both the reduced gluconeogenesis and aminotransferase activities. This is indicated by urea synthesis which was never inferior in the arthritic condition when aspartate was exogenously supplied, being even higher when both aspartate and citrulline were simultaneously present. Possibly, the liver of arthritic rats has a different substrate supply of nitrogenous compounds. This could be in the form of different concentrations of aspartate or other aminoacids such as citrulline or arginine (from the kidneys) which allow higher rates of hepatic ureogenesis.