CONTINUOUS KINETIC DETERMINATION OF PARA-NITROANISOLE O-DEMETHYLATION IN HEMOGLOBIN-FREE PERFUSED RAT-LIVER

Abstract

P-Nitroanisole O-demethylation by perfused rat liver based on the spectral properties of the product, p-nitrophenolate, was determined continuously. Rates of p-nitrophenol production in this system were sensitive to inhibition by CO. p-Nitrophenolate production by livers of normal animals was linear for up to 30 min; rates were only linear for 1-2 min followed by a steady decline in induced (6-fold) livers from phenobarbital-treated rats. Only a small portion (24%) of this steady decline could be accounted for by the formation of conjugation products. Infusion of p-nitrophenol (14 .mu.M) was not associated with a decline in rate. The decline in rate in induced livers was reversed by glucose, suggesting that an intimate relationship may exist between drug and carbohydrate metabolism in the intact liver. Alteration in rates of p-nitroanisole metabolism with various inducing agents of the mixed-function oxidation system (phenobarbital; ethanol) produced parallel changes in rates of hepatic lactate production, most likely reflecting the action of p-nitrophenol to uncouple oxidative phosphorylation. The decline in rate in p-nitroanisole O-demethylation in livers from phenobarbital-treated rats is probably due to reduced availability of NADPH for mixed-function oxidation.