Role of testosterone in the sexual dimorphism of adrenal activity at puberty in the guinea-pig.

Sexual dimorphism in adrenal activity appeared during the pubertal period of the guinea-pig with plasma levels and binding of cortisol lower in male guinea-pigs compared with female, and metabolic clearance rate (MCR) of cortisol higher in male than in female animals. Gonadectomy of female guinea-pigs did not change the values of the parameters regulating adrenal activity. Castration of male guinea-pigs caused a rise in plasma cortisol levels by increasing the binding capacity of transcortin for cortisol and by decreasing cortisol MCR. Treatment of females with testosterone from day 24 produced a drop on day 50 in plasma cortisol levels following a decreased binding capacity of transcortin for cortisol and at the same time as cortisol MCR increased. Furthermore, the adrenal response to stress was higher in castrated than in control males and lower in testosterone-treated females compared with control females. Testosterone appeared to be the hormone responsible for sexual dimorphism in adrenal activity in the pubertal guinea-pig.