Effects of testosterone, hypophysectomy and growth hormone treatment on clofibrate induction of peroxisomal beta-oxidation in female rat liver.

Induction of peroxisomal beta-oxidation by clofibrate under altered hormonal states was investigated in female rat liver. Treatment of rats with clofibric acid (CPIB) caused a significant increase in hepatic peroxisomal beta-oxidation, with female rats being less responsive than males (4.2- vs 12.2-fold increase). However, testosterone treatment following ovariectomy of female rats resulted in an enhanced response to CPIB, giving an induction (11.7-fold) comparable to that seen in male rats. Hypophysectomy of female rats also enhanced the induction (8.2-fold compared with 5.1-fold), suggesting a suppressive effect of a pituitary-dependent factor on CPIB induction of peroxisomal beta-oxidation. Continuous infusion of growth hormone to the hypophysectomized female rats suppressed the enhanced induction nearly to the initial level (6.1-fold). The stimulatory effects of testosterone and hypophysectomy on the enzyme induction were additive. These findings suggest the involvement of growth hormone, as well as male sex hormone, in regulating the responsiveness to CPIB induction of peroxisomal beta-oxidation in rat liver.