Studies on the biliary efflux of GSH from rat liver due to the metabolism of aminopyrine.

The biliary efflux of GSH and GSSG due to aminopyrine was studied using perfused rat livers. The infusion of 0.8 mM aminopyrine led to a rapid rise in the amount of GSH released into the bile with only a small increase in the amount of GSSG released; caval GSH + GSSG efflux was unaffected. N-Benzylimidazole, an inhibitor of cytochrome P-450, completely blocked the response while phenobarbital pretreatment of the rats doubled the rate of GSH efflux. H2O2 and selenium-containing glutathione peroxidase were not involved since livers from selenium-deficient rats perfused with aminopyrine released GSH at the same rate as control livers. Aminopyrine injected i.p. into conscious rats also stimulated biliary GSH efflux to the same extent as with perfused livers. Biliary release of GSH in the perfused livers could be duplicated by infusing formaldehyde. It is proposed that formaldehyde produced during the N-demethylation of aminopyrine by cytochrome P-450 combines reversibly with GSH to form S-hydroxymethylglutathione which is oxidized by formaldehyde dehydrogenase to S-formylglutathione. Formaldehyde formed in excess of its capacity to be metabolized enzymatically is released into the bile as S-hydroxymethylglutathione which then dissociates to its initial reactants.