Pretranslational down-regulation of male specific hepatic P450s after portal bypass.

Diversion of portal blood away from the liver in the portal vein ligated (PVL) male rat results in dysfunction of the hypothalamo-pituitary-gonadal axis, as reflected by an increase in circulating oestradiol, a decrease in serum testosterone and decreased expression of the male-specific cytochrome P450 2C11 in hepatic microsomes. The present study assessed whether there was a decline in the hepatic concentrations of mRNA species corresponding to male-specific P450s and whether female-specific hepatic enzymes may be upregulated after PVL. In microsomes from PVL male rat liver the activities of P450s 2C11 and 3A2 (androstenedione 16 alpha- and 6 beta-hydroxylation, respectively) were decreased to 45% (P < 0.001) and 43% (P < 0.002) of control. Slot blotting revealed a decline in the mRNAs for P450 2C11 and 3A2 to 46 +/- 7 and 27 +/- 4% of respective control (relative to beta-actin mRNA). In contrast, mRNAs for the female specific P450 2C12 and delta 4-ketosteroid-5 alpha-oxidoreductase were unchanged from control (100 +/- 13% and 122 +/- 28%, respectively). P450 2C12 protein was not detected in either control or PVL male rat liver but a slight increase in the rate of 5 alpha-dihydrotestosterone formation was noted after PVL (2.95 +/- 0.40 vs 1.00 +/- 0.22 nmol/min/mg protein, P < 0.05; corresponding, respectively, to 30 and 10% of the activity in female liver microsomes). These studies indicate that the male-specific P450 2C11 and 3A2 are down-regulated at a pretranslational level whereas upregulation of the female-specific enzymes P450 2C12 and delta 4-ketosteroid-5 alpha-oxidoreductase does not occur after PVL. Thus, the endocrine effects of portal bypass result in biochemical demasculinization, but not feminization, of hepatic enzymes involved in steroid biotransformation. Because male-specific P450s are effective steroid hydroxylating enzymes, their down regulation after PVL would significantly decrease hepatic androgen extraction.