Effects of growth hormone on cytochrome P-450j

Hypophysectomy of male and female rats resulted in a 5 and 10-fold increase respectively, in cytochrome P-450j as determined by immunoblotting. Treatment of hypophysectomized rats with growth hormone resulted in a decrease in P-450j. Microsomal N-nitrosodimethylamine demethylase activity was increased approximately 23 and 75 per cent in male and female rats respectively, over the activity in microsomes of intact animals. These studies suggest that hypophysectomy results in an increase in cytochrome P-450j and that growth hormone acts as a repressive factor for constitutive P-450j.