Decrease of valproate-induced hyperammonemia in normal subjects by lipid ingestion

A smaller initial dose protects mice against several lethal doses of ammonium acetate

The synthesis of urea in the liver is the main mechanism for the elimination of excess ammonia. Rapid stimulation of the synthesis of urea (e.g. by administration of carbamyl glutamate, the analog of the physiological activator of carbamyl phosphate synthetase I) protects animals given lethal doses of ammonia. Since ammonia enhances the activity of the urea cycle, we tested and show here that administration of small doses of ammonium acetate supresses the mortality induced by a series of repeated LD100 of ammonium acetate separated by one hour, when the first LD100 is injected i.p. starting from 30 min to 5 hours after the initial smaller dose of ammonium acetate. Under these conditions, the levels of ammonia in blood are elevated more than ten times, but in spite of the greater amount of ammonia administered, the ammonemia is much lower than in mice dying after a single LD100. The enhanced synthesis of urea observed is correlated with an increase in the intramitochondrial content of N-acetyl glutamate. These findings are of interest as far as the short-term regulation of urea cycle, the mechanism of ammonia toxicity and have clinical implications.

Effect of valproate on renal metabolism in the intact dog

Valproate is an antiepileptic drug known to induce hyperammonemia in humans. This hyperammonemia might result from a reduced detoxification of ammonium in the liver and/or from an accelerated renal ammoniagenesis. Six dogs with normal acid-base equilibrium and eight dogs with chronic metabolic acidosis were infused with valproate directly into their left renal artery in order to obtain arterial concentrations around 3 to 4 mM. The arterial ammonium concentration rose only in chronically acidotic dogs, whereas the lactate concentration and the lactate/pyruvate ratio increased in both groups. The urinary excretion of lactate and pyruvate increased markedly but the urinary excretion of other relevant metabolites remained minimal. Renal glutamine utilization and ammonium production were not changed by valproate administration in normal dogs but increased modestly in acidotic dogs. However, renal lactate utilization was drastically reduced and in fact, changed into a net production of lactate. Valproate strikingly reduced the renal cortical concentrations of glutamine, glutamate, alphaketoglutarate and citrate, and more modestly those of malate, oxaloacetate, aspartate, alanine and ATP. By contrast, the tissue lactate concentration and the lactate/pyruvate ratio were markedly increased. In experiments with brush border membrane vesicles, valproate inhibited the lactate transporter. These results suggest that high concentrations of valproate drastically inhibited the proximal reabsorption and the proximal and distal oxidation of lactate and pyruvate. Valproate probably became itself a significant energetic substrate for the kidney.