Maturational changes in adrenal xenobiotic metabolism in male and female guinea pigs.

In young (25-day-old) guinea pigs, adrenal and hepatic benzo[a]pyrene (BP) hydroxylase activities were similar but the rates of ethylmorphine (EM) demethylation were greater in adrenals than liver. Between 25 and 50 days of age no sex differences in adrenal or hepatic enzyme activities were demonstrable. The rates of adrenal BP and EM metabolism increased with age in guinea pigs of both sexes; activities reached significantly higher levels in males than females. In contrast, hepatic metabolism of BP and EM declined with maturation and activities were similar in males and females at all ages. Neither microsomal cytochrome P-450 concentrations no NADPH-cytochrome c reductase activities correlated with the maturational changes or sex differences in xenobiotic metabolism. Adrenal microsomal steroid 21-hydroxylase activity did not change significantly with aging and was not sex-dependent. The results indicate that opposite changes occur in adrenal and hepatic xenobiotic metabolism as a function of aging, resulting in substantially greater adrenal than hepatic activity in sexually mature animals. The data also suggest that adrenal microsomal drug and steroid metabolism are independently regulated.