The effects of neonatal androgenization of male rats on testosterone metabolism by the hypothalamus-pituitary-gonadal axis

Male rats were androgenized on the third postnatal day by a single injection of 1 mg testosterone propionate. The in vitro metabolism of [4- 14C]testosterone by pituitary and hypothalamus homogenates was investigated at the age of 90 days. The pituitary and hypothalamus homogenates from control and neonatally androgenized animals converted [4- 14C]testosterone to the same metabolites, mainly 5α-reduced derivatives; the quantitative yield of 5α-reduced metabolites was much higher in the pituitary homogenates of androgenized rats. The hypothalamic homogenates showed no differences. In the androgenized rats a very significant increase of the plasma FSH levels was measured while the LH levels were also augmented. The plasma levels of testosterone were not different from the values in control rats, notwithstanding a 25% reduction in testes weight. The present experiments appear to indicate that the neonatal androgenization results in an accentuation of the sexual dimorphism which normally exists in the pituitary of adult rats for the 5α-reductase activity.