VALPROIC ACID - BRAIN AND PLASMA-LEVELS OF THE DRUG AND ITS METABOLITES, ANTICONVULSANT EFFECTS AND GAMMA-AMINOBUTYRIC ACID (GABA) METABOLISM IN THE MOUSE

  • 1 January 1982
    • journal article
    • research article
    • Vol. 220  (3) , 654-659
Abstract
The slow onset and carry-over effect of valproic acid (VPA) therapy observed in some clinical and experimental animal studies were examined by parallel pharmacokinetic and pharmacological investigations in a mouse model. VPA was rapidly transferred into brain and was cleared from that tissue with rates which exceeded plasma clearance rates. Of several VPA metabolites present in plasma, only 2-propyl-2-pentenoic acid could be found in the brain. This metabolite was cleared from plasma and from brain slower than the parent drug. GABA concentrations were increased within 15 min after VPA injection and remained significantly elevated for at least 8 h. A similar time course was found in regard to the increase of the electroconvulsive threshold (maximal seizures) induced by VPA administration. The activity of glutamic acid decarboxylase rose parallel to the elevation of brain GABA levels, whereas the activity of GABA aminotransferase was not affected. Whereas the rapid onset of the effect on electroconvulsive threshold and on GABA metabolism can be explained by the rapid entrance of VPA into brain, the carry-over effects observed correlated with the kinetics of the metabolite 2-propyl-2-pentenoic acid better than with those of VPA due to the persistence of this metabolite in brain.