The regulation by growth hormone of microsomal testosterone 6 beta-hydroxylase in male rat livers.

The relationship between growth hormone and testosterone (T) 6 beta-hydroxylase was investigated in normal and hypophysectomized (hypox) male rats. The administration of human growth hormone (hGH) by either intermittent injections or continuous infusion to normal and hypox rats decreased the activity of T 6 beta-hydroxylase in hepatic microsomes. Hypophysectomy did not reduce, but rather increased the 6 beta-hydroxylase activity, while the 16 alpha-hydroxylase activity decreased. These results, together with the data from a Western blot, indicate that growth hormone acts as a repressive factor for the expression of T 6 beta-hydroxylase in a manner different from the regulation of T 16 alpha-hydroxylase.