Effect of glucagon and phorbol myristate acetate on oxidative demethylation and lipid peroxidation in isolated hepatocytes.

Oxidative demethylation of aminopyrine and peroxidation of endogenous lipids induced by cumene hydroperoxide were studied in hepatocytes isolated from fed male rats. Glucagon and phorbol-12-myristate-13-acetate (PMA) inhibited both processes in the concentration-dependent manner. Pretreatment of hepatocytes with 1 microM glucagon decreased oxidative demethylation by 75% and had a much smaller effect on lipid peroxidation. Preincubation with 1 microM PMA inhibited both processes by 25-30%. Phosphorylation of three isoforms of cytochrome P-450 was observed in microsomes isolated from hepatocytes incubated in the presence of [32P]orthophosphate. After incubation with PMA the phosphorylation of all these proteins was increased by 60-100%, whereas glucagon increased the phosphorylation of only one isoform. Consequences of the phosphorylation of various isoforms of cytochrome P-450 for metabolic functions of the monooxygenase system are discussed.