Expression of hepatic microsomal cytochrome P450s as altered by uremia

The proportions of different hepatic microsomal cytochrome P450s expressed in uremic rats were studied with specific antibodies and with a steroid hydroxylase assay. In male uremic rats, the hepatic levels of P450 2C11, a male-specific form, and 3A2, a male-dominant form, were decreased to about 30% at 5 weeks after the induction of uremia. These changes were paralleled by decreases in the activities of testosterone 2 alpha-, 16 alpha-, and 6 beta-hydroxylation. The level of P450 2A1, abundant in immature rats, was increased 2-fold by uremia and accompanied by an increase in testosterone 7 alpha-hydroxylation activity. The levels of P450 2C6 and 2E1 were not changed by uremia. The levels of male-specific and male-dominant forms such as P450 2C11 and 3A2 are affected by the serum level of testosterone, which was decreased in the male rats with uremia. Therefore, castrated rats were prepared to compare the effects of testosterone on hepatic cytochrome P450s in uremic rats with those in castrated rats. When testosterone was administered to the castrated rats, the decreased levels of both P450 2C11 and 3A2 returned to normal. However, the administration of testosterone to the uremic rats did not prevent the decrease in the levels of these P450s. In female rats, changes in the levels of cytochrome P450s were not as great during uremia as those in male uremic rats. The level of P450 2C12, a female-specific form, was not changed; the level of P450 2A1 was increased by 50%, that of 3A2 which is barely detected in female rats was increased by 60%, and that of 2E1 was increased by 25%. These results suggested that the changes in the hepatic levels of cytochrome P450s were affected by factors other than testosterone in uremic rats.