Abstract

• A variety of compounds including drugs, carcinogens, steroids and fatty acids are metabolized by microsomal monooxygenase system in the liver. The effect of phenobarbital(PB) on the monooxygenase system in the liver microsomes of neonatal, immature- and adult-rats of both sexes were investigated. In the liver microsomes of rats, the activities of cytochrome P-450, NADPH-cytochrome C reductase, cytochrome b₅, NADH-cytochrome C reductase, p-nitroanisole-O-demethylase and the formation of lipid peroxide were assayed : the following results were obtained. 1) In the liver microsomes of rats, the activities of cytochrome P-450 and NADPH-cytochrome C redutase were increased in PB treated rats compared to control. Among the developmental stages, the contents of hepatic microsomal cytochrome P-450 and NADPH-cytochrome C reductase were highest in the female adult rat and the male immature rat. 2) The contents of hepatic microsomal cytochrome b₅ and NADH-cytochrome C reductase were increased in PB treated rats compared to control. Among the developmental stages the content of hepatic microsomal cytochrome b₅ was highest in the female adult rat and the male immature rat, whereas the content of hepatic microsomal NADH-cytochrome C reductase was highest in the adult rats of both sexes. 3) The formation of lipid peroxide was increased in PB treated rats compared to control. Among the developmental stages the formation of lipid peroxide was highest in the female adult rat and the male immature rat. 4) The activity of hepatic microsomal p-nitroanisole-O-demethylase was increased in PB treated rats compared to control. Among the developmental stages the activity of p-nitroanisole-O-demethylase was highest in the female adult rat and the male immature rat.