Studies on distribution and metabolism of valproate in rat brain, liver, and kidney

Time-course studies on the distribution and metabolism of valproate (VPA) in rat brain, liver, and kidney, after intraperitoneal injection of a mixture of [14C]VPA and [3H]VPA, showed that: (1) maximal amount of radioactivity in the various tissues was observed after 30 min from the time the drug was administered; (2) at 30 min the distribution of labeled VPA in brain, liver, and kidney was 17%, 64%, and 19% of the total radioactivity, respectively; (3) at 24 hr more than 97% of the total radioactivity was lost from the tissues and the 14C/3H ratios increased significantly with time. Studies on the regional distribution of the drug showed that it is relatively homogeneously distributed. Studies on the subcellular distribution of the drug showed that it is associated mostly with the soluble and mitochondrial fractions, with little radioactivity in the myelin and symaptosomal fractions. Radiochromatography of VPA metabolites in perchloric acid extracts from brain, liver, and kidney revealed the presence of four metabolites. VPA was not incorporated into phospholipids of the neuronal membranes. Furthermore, it had no significant effects on Mg2+-ATPase and (Na+ + K+)-ATPase in synaptosomes and microsomes obtained either from control or from rats injected with VPA. It was concluded that this antiepileptic drug does not appear to act through its incorporation into neuronal membrane or through its action of the Na+ pump.