Effect of the convulsive agent 3-mercaptopropionic acid on the levels of GABA, other amino acids and glutamate decarboxylase in different regions of the rat brain

Intraperitoneal injection of 3-mercaptopropionic acid into rats caused severe convulsions which started after about 7 min. Of the amino acids examined only the level of GABA changed after 4 min and immediately before (6.5–7 min) the convulsions started. The decrease in GABA concentration detected immediately before the onset of convulsions was about 35 per cent in the cerebral cortex, corpus striatum and cerebellum, 30 per cent in pons-medulla and 20% in hippocampus. Concomitant with the fall in GABA there was a large, reversible inhibition of glutamate decarboxylase activity in the brain. The uptake of GABA into synaptosomes isolated after injection of the convulsive agent was not reduced, and the uptake of GABA into synaptosomes was not inhibited by high concentrations of 3-mercaptopropionic acid added in vitro. During convulsions levels of aspartate and taurine decreased significantly in all the brain regions investigated. A small increase in glutamine was detected in pons-medulla and in cerebellum. Major changes in the concentrations of other amino acids such as glutamate, alanine, serine and glycine were found only in corpus striatum.     

GABA turnover in the brain of rat lines developed for differential ethanol-induced motor impairment

The role of GABAergic neurons in the differential sensitivity to ethanol between the AT (Alcohol Tolerant) and ANT (Alcohol Nontolerant) rat lines developed for low and high degree of motor impairment from ethanol, was studied by comparing the effect of ethanol (2 or 4 g/kg, IP) on GABA turnover in different regions of the brain in these rat lines. GABA turnover was estimated from the accumulation of GABA after inhibition of GABA aminotransferase with aminooxyacetic acid (AOAA, 50 mg/kg, IP) given 10 min after administration of ethanol. The rats were killed two hours after the AOAA treatment with focused microwaves. The concentrations of GABA, aspartate, glutamate, glutamine and taurine were analyzed with HPLC. The saline-treated ANT rats were found to have a higher concentration of GABA in the striatum and a higher rate of GABA accumulation in the cerebellum than the AT rats. Ethanol suppressed the accumulation of GABA in both lines, but the suppression was significantly greater in the AT rats than in the ANT rats. In specific regions, this line difference was significant in the cerebral cortex and cerebellum with the higher ethanol dose. No line differences were found in the brain or tail blood ethanol concentration. AOAA increased the concentration of glutamine, decreased that of aspartate and glutamate, and did not modify that of taurine. The AOAA-induced changes in the concentrations of these amino acids were, however, minor relative to those found in the concentrations of GABA. The results that GABAergic mechanisms are involved in the differential sensitivity to the motor-impairing effects of ethanol between the AT and ANT rats.     

Effect of ethanol concentration on rates of ethanol elimination in normal and alcohol-treated rats in vivo.

Ethanol was infused intravenously to yield in the blood concentrations between 30 and 40 mM (low dose) or 80 and 90 mM (high dose). Duplicate blood samples were taken every 30 min for gas Chromatographie determination of ethanol. Elimination curves for both low and high does of ethanol were linear in normal rats until ethanol concentrations reached values of less than 5 mM. At the low and high doses, average rates of ethanol elimination were 179 ± l and 266 ± 13 μmoles/g/hr respectively. The stimulation of ethanol metabolism due to the high dose did not diminish as the concentration declined. At both doses in both normal and ethanol—pretreated rats, elimination rates were diminished over 80 per cent by prior treatment with 4-methylpyrazole. Pretreatment with aminotriazole produced a 20–25 per cent decrease in the rate at the high dose in normal rats and at both doses in ethanol-pretreated rats, but had no effect at the low dose in normal rats. From these data we conclude that a concentration effect of ethanol on rates of ethanol elimination, which has both an alcohol dehydrogenase—and a catalase-H₂O₂-dependent component, exists in vivo. Moreover, the adaptive increase in ethanol elimination due to chronic pretreatment with ethanol also involves both components. Pyruvate and ethanol pretreatment stimulated ethanol elimination at the low but not at the high dose of ethanol. It is further concluded that NADH reoxidation is rate-limiting for ethanol utilization at the low dose whereas the activity of alcohol dehydrogenase becomes limiting at the high dose and after pretreatment with ethanol in the fed state in vivo.     

Relationships between in vivo and in vitro inhibition of acetylcholinesterase (AChE) and impairment of neuromuscular transmission in the rat phrenic-nerve diaphragm by a tertiary anticholinesterase and its quaternary analogue

The tertiary anticholinesterase agent pinacolyl S-(2-dimethylaminoethyl) methylphosphonothioate (compound I) and its quaternary analogue (compound II), were administered subcutaneously to atropinized rats. The animals were killed 30 min later and the tension of the isolated phrenic nerve-diaphragm preparation, stimulated indirectly at 100 Hz for 10 sec, was compared with that of preparations from control animals. A dose of 1.5 μmole/kg of the quaternary compound II, which has a bimolecular rate constant of inhibition twice that of the tertiary compound I, reduced the tetanic response of the diaphragm by 50 per cent; the equivalent dose of the tertiary compound I was 5.2 μmole/kg. At these dose levels, compound II inhibited 65 per cent of the diaphragm acetylcholinesterase (AChE) activity, determined on homogenates, and compound 192 per cent. When the phrenic nerve-diaphragm preparation from untreated animals was incubated for 20 min with various concentrations of compound I or II, the rate of enzyme inhibition conformed approximately to first order kinetics and equimolar concentrations of the inhibitors reduced tetanic tension to 50 per cent in the same time. There was no discontinuity in the plot of per cent AChE inhibition vs logarithm of the concentration of compound I or II but the slope was much less with the quaternary compound II. The results provide additional evidence that quaternary compounds can reach all sites with AChE activity only in vitro and that their distribution when applied in vitro is not the same as that in vivo.     

Correlation of glutamate plus aspartate dose, plasma amino acid concentration and neuronal necrosis in infant mice

Eight-day-old mice were given by gavage glutamate and aspartate mixtures providing each amino acid at 125, 250 or 500 mg/kg body weight (250, 500 and 1000 mg total dicarboxylic amino acids/kg) and the degree and extent of neuronal necrosis were determined. Similar studies were carried out in mice given monosodium L-glutamate at 250 or 500 mg/kg body weight. Plasma aspartate and glutamate concentrations were determined at each dose level. No animal given either glutamate or the glutamate plus aspartate mixture at 250 mg/kg developed neuronal necrosis. However, neuronal necrosis developed in 30% of animals given glutamate at 500 mg/kg (12+/-2 necrotic neurons/section in the region of maximal damage) and in 17% of animals given 250 mg glutamate/kg plus 250 mg aspartate/kg (11-13 necrotic neurons/section in the region of maximal damage). The threshold mean peak plasma glutamate plus aspartate concentration associated with neuronal necrosis was 128+/-24 mumol/dl. Using these data, and previously published data for aspartate-induced neurotoxicity (Finkelstein et al. Toxicology 1983, 29, 109), the individual threshold plasma glutamate and aspartate concentrations associated with neuronal necrosis were calculated to be 110 mumol/dl for aspartate and 75 mumol/dl for glutamate.     

The fate of the ethanol analogue 1,3-butanediol in the dog. An in vivo-in vitro comparison

In view of the current interest in 1,3-butanediol as food additive or potential drug its pharmacokinetics have been investigated in the dog and compared to its oxidation in vitro by alcohol dehydrogenase. Plasma disappearance of i.v. doses of 5.5 mmol/kg were zero order followed by first order. Assuming Michaelis-Menten kinetics a V_max of 1.23 ± S.D. 0.27 μmol/min/g of liver and a K_m of 1.15 ± 0.85 mM could be calculated. The corresponding values for 1,3-butanediol metabolism by alcohol dehydrogenase in vitro were 1.62 ± 0.34 μmol/min/g of liver and 5.11 ± 1.45 mM. Hepatic vein catheterizations were used to measure hepatic blood flow (18.1 ± 2.8 ml/min/kg) and the fraction of butanediol disappearing in the liver, which was only 34.2 ± 6.6 per cent. Compared to ethanol, V_max of 1,3-butanediol was 15 per cent smaller in vitro, 45 per cent smaller in vivo, K_m was 3 times larger in vitro and 60 per cent smaller in vivo. The splanchnic elimination fraction of 1,3-butanediol was about $\text{1}\text{2}$ the one of ethanol. These data are consistent with the concept, that oxidation by alcohol dehydrogenase is the major route of butanediol elimination. The differences between 1,3-butanediol and ethanol metabolism, however, render different pharmacological and toxicological effects likely.     

The effects of salicylate on the concentrations of amino-acids in mouse tissues

The concentrations of amino-acids in chopped preparations of mouse liver incubated with 0 to 20 mM salicylate were measured. The changes, observed with salicylate concentrations of 10 mM and above, were increased concentrations of aspartate, glutamine, tyrosine and ornithine and decreased concentrations of glutamate and γ-aminobutyrate. The effects of the intraperitoneal injection of salicylate, in doses ranging from 75 to 600 mg/kg body weight, on the amino-acid concentrations in mouse blood, kidney, liver and brain were studied. With a dose of 600 mg/kg, the amino-acid concentrations were decreased in the blood (except glutamate and aspartate which increased) and in the kidney, were increased in the liver (except glutamine, glutamate, glycine and alanine which decreased) and were unchanged in the brain (except alanine, valine and leucine which decreased and γ-aminobutyrate which increased). These changes may result from a combination of an inhibitory effect of salicylate on the renal tubular transport of the amino-acids and intracellular actions of the drug on aminotransferase and other enzyme activities.     

Mechanism of the effect of acute ethanol on hexobarbital metabolism

The effect of acute ethanol treatment on hepatic metabolism of hexobarbital (Hb) was studied in the rat. Oral administration of 3 g/kg of ethanol (15% w/v) inhibited Hb hydroxylase activity 45–50 per cent. A dose-response relationship was found for ethanol inhibition of Hb metabolism. The overall hepatic microsomal protein content was not affected, but the hepatic cytochrome P-450 level was reduced approximately 42 per cent by this ethanol treatment. Corticosterone (12.5 mg/kg, i.p.) inhibited Hb hydroxylase activity 43 per cent. The combination of ethanol and corticosterone treatment further inhibited Hb hydroxylase activity. Study in vitro showed that corticosterone inhibited Hb metabolism competitively. Ethanol caused a 3-fold increase in the plasma corticosterone level but had no effect on plasma corticosterone of adrenalectomized rats. Hexobarbital metabolism was not affected by ethanol in adrenalectomized rats. Thus, the inhibition of hepatic Hb metabolism by acute ethanol was caused by the increased release of corticosterone induced by ethanol.     

An in vivo insight to the toxicological profile of various organotellurides

In this study we have examined the in vivo toxic effects of various organochalcogens on hepatic, renal, glycemic and lipid profile. Diorganotellurium dichloride phosphonate (C1) at all tested doses did not modify serum alanine aminotransferase (ALT) activity in mice. While, 2-butyltellurium furan (C2) and dinaphthalene ditelluride (C3) at a dose of 0.75 and 0.125 mmol/kg caused an increase in aspartate aminotransferase (AST) and ALT activities. Our data showed that C1 caused an increase in urea content at different doses while treatment with C2 and C3 did not modify urea content. Treatment with C2 caused a significant alteration in serum glucose and fructosamine levels which explains the possible toxicity of these compounds. No significant changes were observed for cholesterol and triglycerides levels. These results suggest that organochalcogen compounds presented liver and renal toxicity and also altered glycemic profile which may leads to various clinical complications.     

Effects of pyrazole and 3-amino-1,2,4-triazole on methanol and ethanol metabolism by the rat

The metabolism of methanol-¹⁴C and ethanol-1-¹⁴C in rats was evaluated from the rates of ¹⁴CO₂ production. 3-Amino,1,2,4-triazole, a known catalase inhibitor, decreased by 10 and 35 per cent the rates of oxidation of ethanol and methanol, whereas pyrazole, an alcohol dehydrogenase inhibitor, decreased the rates 85 and 50 per cent respectively. However, the simultaneous use of both inhibitors gave the same effects produced by pyrazole alone. Thus the relative contributions in vivo to alcohol metabolism of rat liver alcohol dehydrogenase and catalase-mediated peroxidation, cannot be estimated only in this way. Rat liver alcohol dehydrogenase was purified 14·7 times. At pH 7·0 and 30°, the K_m for methanol was 340 mM and for ethanol 0·26 mM. The V_max/e was 2·36 nM for methanol and 22·3 nM for ethanol (NADH × U^?1 × 1^?1 × sec^?1). 3-Amino-1,2,4-triazole inhibited the purified enzyme with a K_i of 55 mM for methanol and 33 mM for ethanol. The K_i of pyrazole was 2·3 mM for methanol and 2·2 mM for ethanol. The amount of alcohol dehydrogenase present in rat liver, with the found kinetic constants, can account for the ethanol oxidation in vivo, but fails to account, as methanol dehydrogenase, for the observed pyrazole-sensitive methanol oxidation. A mechanism for the complete oxidation of methanol to CO₂ and water through the concerted action of catalase and alcohol dehydrogenase is suggested. 3-Amino-1,2,4-triazole in a dose of 1 g/kg decreases more than 90 per cent of the catalatic activity of catalase, but under certain conditions in vitro, only about 50 per cent of the peroxidative activity of catalase towards methanol and ethanol. Consequently, the degree of catalase-mediated peroxidation should not be controlled or estimated from the residual catalatic activity when using catalase inhibitors. Pyrazole, at a dose of 0·3 g/kg, does not affect catalase activity 1 hr after administration, but decreases it more than 90 per cent after 24 hr. This effect is completely prevented in the presence of alcohol.     

Effect of carbon tetrachloride treatment on ethanol metabolism

Administration of a single dose (2.5 ml/kg body weight, p.o.) of carbon tetrachloride to rats was found to cause a marked decrease in activity of the hepatic microsomal ethanol oxidizing system (MEOS). As early as 6 hr after CCl₄ administration 50 per cent decrease of MEOS activity was observed; this decrease amounted to 58 and 63 per cent at 10 and 20 hr respectively. With identical CCl₄ treatment, there was no change in hepatic alcohol dehydrogenase activity. At 20 hr, when the reduction of MEOS was greatest, there was no significant effect of the CCl₄ on the rate of ethanol uptake by liver slices or on the rate of ethanol metabolism in vivo as measured in the whole body or as estimated from the rate of decrease of blood ethanol concentration. It is, therefore, suggested that MEOS does not play a significant role in ethanol metabolism in vivo in the rat.     

Altered time course of changes in the hippocampal concentration of excitatory and inhibitory amino acids during kainate-induced epilepsy

The temporal sequence of electrophysiological and biochemical correlates of epilepsy induced by systemic injection of kainic acid (15 mg/kg i.p.) was investigated in male rats. A significant decrease in the hippocampal concentration of glutamate and aspartate was observed 20 min after the injection. These decreases preceded both electrographic and behavioral manifestations of epilepsy, thus suggesting a causal relationship between acidic amino acid changes and the genesis of kainate-induced hyperactivity. About 30-45 min after kainate injection, a decrease in glutamate, aspartate, glycine and taurine and no change in GABA concentration were observed. Bioelectrical activity, recorded in the regio inferior (CA3) of the hippocampus or in the fascia dentata revealed the presence of high frequency bursts separated by a long-lasting depression of discharge. About 55-75 min after the injection, the number of spikes in each burst increased and the duration and frequency of interictal pauses decreased. This stage was characterized by a decrease in glutamate and aspartate, restoration to normal of glutamine, glycine and taurine and a decrease in GABA.     

Pharmacological and biochemical actions of the hemolytic agents acetylphenylhydrazine and phenylhydrazine on monoamine oxidase in the rat

The injection of normal rats with the hemolytic agents acetylphenylhydrazine (APHZ) and phenylhydrazine (PHZ) rapidly produces a long-lasting inhibition of monoamine oxidase (MAO). The effect is more pronounced in liver than in brain at the dosage levels used, viz. 80 mg/kg body weight. APHZ inhibits liver MAO more actively than does an equivalent dose of PHZ. The former compound causes 65–75 per cent inhibition of activity by 24 hr after injeption, whereas PHZ inhibits by about 40 per cent at 24 hr and 50 per cent at 2 days. On the other hand, PHZ is slightly more active than APHZ against the rat brain enzyme in vivo. Equal doses of PHZ and APHZ cause 39 and 30 per cent inhibition, respectively, after 2 days. The inhibitory effects of APHZ in vivo are enhanced in riboflavin-deficient rats. Both drugs inhibit MAO in vitro in an immediate, irreversible, non-competitive manner; inhibition is independent of pH. PHZ is more active than APHZ against rat liver MAO. Concentrations of the respective chemicals which cause 50 per cent inhibition in vitro after 15 min of pre-incubation with the enzyme at 37° and pH7.0 are about 1.6 × 10^?5 M and 3.6 × 10^?5 M. Kynuramine protects MAO against inhibition by APHZ but not PHZ. Cyanide is active in enhancing the inhibitory action of both substances on MAO in vitro.     

Concentration-dependent ethanol metabolism in perfused liver

Ethanol at initial concentrations of 9.7, 32.5 and 52 mM was added to a recirculating liver perfusion system in the absence of added substrate. A concentration-dependent increase in ethanol metabolism was observed in perfused liver. The β-hydroxybutyrate/acetoacetate ratio (B/A) increased on addition of a low ethanol concentration (9.7mM). The ratio, however, declined at the higher concentration (52 mM). The decline has been reported previously by others in in vivo studies in the rat. Addition of 10 mM L-alanine to the perfusate increased ethanol metabolism, oxygen consumption and urea formation. The concentration-dependent increase in ethanol metabolism and the decline in B/A ratio did not occur in the presence of alanine. Ethanol metabolism in the presence and absence of alanine was completely blocked by 4-methylpyrazole. The changes in B/A ratio were likewise blocked. It is postulated that the concentration-dependent increase in ethanol metabolism is dependent on the alcohol dehydrogenase pathway. The concentration-dependent increase in ethanol metabolism observed under in vitro conditions was previously reported not to occur in vivo. Since the additon of alanine to the perfusate blocked the concentration-dependent ethanol metabolism, it would appear that the primary difference between in vivo and in vitro observations is the absence of adequate energy substrates under in vitro conditions. Possible mechanisms for the elevated ethanol metabolism under in vitro conditions are discussed.     

Ethanol enhancement of cocaine-induced hepatotoxicity

Ethanol administration (4.3% ethanol in a liquid diet for 5 days) to adult male mice produced a peak blood ethanol concentration of 180 mg/100 ml and resulted in a significant increase in hepatic cytochrome P-450 levels. Ethanol treatment significantly reduced cocaine-induced acute lethality from 67 to 23 per cent. However, ethanol treatment resulted in a potentiation of a latent (1–7 day) cocaine-induced toxicity characterized by hepatic dysfunction, as monitored by serum glutamate-pyruvate transaminase (SGPT) activity, and a profound centrilobular necrosis. The minimum dose of cocaine that caused elevations of SGPT activity was 20 mg/kg, i.p.; maximum elevations of SGPT activity were produced by a dose of 40 mg/kg, i.p. The peak elevations of SGPT activity were seen between 24 and 30 hr following adminstration of cocaine. Frank hepatic necrosis was seen following administration of 30 mg/kg of cocaine. Ethanol potentiation of cocaine-induced hepatoxicity was dependent on induction of the hepatic cytochrome P-450 mixed function oxidase enzyme system. The intralobular location of the cocaine-induced hepatic necrosis was also dependent upon the inducing agent used. Ethanol potentiated the cocaine-induced delayed toxicity presumably by enhancing its biotransformation to a chemically reactive intermediate metabolite that produced the hepatic centrilobular necrosis.     

Protective effect of diphenyl diselenide on acute liver damage induced by 2-nitropropane in rats

The effect of diphenyl diselenide, (PhSe)2, administration on 2-nitropropane (2-NP)-induced hepatic damage was examined in male rats. Rats were pre-treated with a single dose of diphenyl diselenide (10, 50 or 100 micromol/kg). Afterward, they received only one dose of 2-NP (100 mg/kg body weight dissolved in olive oil). The parameters that indicate tissue damage such as plasma alanine aminotransferase (ALT), aspartate aminotransferase (AST), gamma-glutamyl transferase (GGT), alpha-fetoprotein (AFP), creatinine and urea were determined. Since toxicity induced by 2-NP is related to oxidative stress, lipid peroxidation was also evaluated. Diphenyl diselenide (100 micromol/kg) significantly reduced plasma ALT, gamma-GGT, AFP levels when compared to 2-NP group. Treatment with diphenyl diselenide, at all doses, effectively protects the increase of lipid peroxidation when compared to 2-NP group. Histological examination revealed that 2-NP treatment causes a moderate swelling and degenerative alterations on hepatocytes and diphenyl diselenide (100 micromol/kg) protects against these alterations. Diphenyl diselenide (50 and 100 micromol/kg) significantly decreased the urea level. This study evidences the protective effect of diphenyl diselenide by 2-NP-induced acute hepatic damage.     

Comparison of the activity of 2'-deoxycoformycin and erythro-9-(2-hydroxy-3-nonyl)adenine in vivo.

The inhibition of P388 cell deamination of arabinosyladenine (ara-A) in vivo by the adenosine deaminase inhibitors 2′-deoxycoformycin (dCF) and erythro-9-(2-hydroxy-3-nonyl)adenine (EHNA) and their subsequent effects on ara-A metabolism were determined and compared. A single i.p. injection of EHNA (3 mg/kg, 10.9 μmoles/kg) initially inhibited ara-A deamination in vivo by 96 per cent with recovery to 50 per cent of control values within 30 min. In comparison, dCF (0.2 mg/kg, 0.75 μmole/kg) inhibition of ara-A deamination was initially low (4 per cent), but maximized (96 per cent) after 15 min. This inhibition was sustained for 2 hr and did not recover to 50 per cent of control values until after 10 hr. Injected alone, the $\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ of ara-A in the peritoneal ascitic fluid was less than 1 min, but was increased to 7 min when injected with EHNA and to 12 min when injected 15 min after dCF. The rate of efflux of ara-A and its metabolites from the peritoneal cavity ($\text{T}{}_{\mathrm{<mtext>case1</mtext><mtext>2</mtext>}}\text{= 15?18}\text{min}$) was not affected significantly by either deaminase inhibitor. Cellulat ara-ATP concentrations were elevated and the extent and duration of inhibition of DNA synthetic capacity were increased identically in cells of mice treated with ara-A and either deaminase inhibitor as compared with those treated with ara-A alone. Sustained deaminase inhibition after intraperitoneal concentrations of ara-A had been diminished by otherwise normal disposition did not augment the biochemically demonstrable activity of ara-A. Therefore, it appears that maintenance of the initial high concentrations of ara-A is the primary function of a deaminase inhibitor in increasing the therapeutic efficacy of this analog.     

Evaluation of Moxifloxacin-induced Biochemical Changes in Mice

The aim of the present study was to investigate the toxicological effects of moxifloxacin in mice to determine the toxicological implications. Forty mice of both sexes were divided into four groups of 10 mice each, designated as A, B, C and D. Group A served as the control and received 2 ml of distilled water, while Groups B, C and D were orally administered 12.5, 25 and 50 mg/kg body weight of moxifloxacin once daily for 7 days, respectively. The weights of the mice were recorded before and throughout the duration of drug administration. Blood samples were collected for serum analysis. Total blood protein, cholesterol, triglyceride, creatinine, activities of aspartate transaminase, alanine transaminase and alkaline phosphatase, levels of high density lipoprotein-cholesterol and low density lipoprotein-cholesterol were assayed. There were significant (P≤0.05) differences in the concentrations of serum creatinine, urea, aspartate transaminase, alanine transaminase and alkaline phosphatase, levels of high density lipoprotein-cholesterol, low density lipoprotein-cholesterol, cholesterol and triglyceride of mice administered moxifloxacin. Serum level of total bilirubin in low dose treated animals was not significantly different from that of the control group animals, but there were significant dose dependent decrease in the animals treated with 25 mg/kg as well as 50 mg/kg. Data of the study indicate there was a dose dependent reduction in the protein metabolites, lipid profile and liver enzyme activities of mice administered moxifloxacin.     

Stimulation of glutamine metabolism by the antiepileptic drug, sodium valproate, in isolated dog kidney tubules

The effects of sodium valproate, a widely used antiepileptic drug and an hyperammonemic agent, on glutamine and glutamate metabolism were studied in isolated dog kidney tubules. Valproate markedly stimulated glutamine removal as well as the formation of ammonia, aspartate, pyruvate, lactate, alanine and glucose; the increase in ammonia formation was explained by a stimulation by valproate of flux not only through glutaminase (EC 3.5.1.2) but also through glutamate dehydrogenase (EC 1.4.1.3). By contrast, valproate did not stimulate glutamate removal or ammonia, aspartate and glucose formation from glutamate; this suggests that the increase in flux through glutamate dehydrogenase with glutamine as substrate was secondary to the increase in flux through glutaminase. Accumulation of pyruvate, alanine and lactate in the presence of valproate was much less from glutamate than from glutamine. Inhibition by amino-oxyacetate of accumulation of aspartate and alanine from glutamine caused by valproate did not prevent the acceleration of glutamine utilization and the subsequent stimulation of ammonia formation. These data are consistent with a stimulatory effect of valproate primarily exerted at the level of glutaminase in dog kidney tubules. However, the fact that assayed activity of glutaminase remained unchanged in the presence of valproate suggests that this compound accelerates flux through the latter enzyme by an indirect mechanism probably related to the renal metabolism of this compound.