The effect of neonatal castration of male rats on the level of sex-hormone receptors in the hypothalamus and hypophysis of adult animals.

The concentration of oestradiol (E2) and testosterone (T) cytosolic and nuclear receptors was studied in the pituitary and hypothalamus of adult male rats gonadectomized either on the first day after birth (long-term castrates) or in adulthood (short-term castrates). Intact male rats and short-term castrates had the same levels as each other of cytosolic and nuclear oestrogen and androgen receptors in the pituitary, mediobasal hypothalamus (MBH), and preoptic anterior hypothalamus (POAH). In neonatally castrated males the number of nuclear T-binding sites in the pituitary and both areas of the hypothalamus decreased, whereas the number of nuclear E2-receptors was reduced only in the MBH. The number of E2-receptors in the POAH of such animals increased. The number of E2- and T-binding sites in the nuclear fraction of the MBH and POAH was the same in long-term castrates whether they did not receive testosterone propionate (TP) or received it from 7 days after birth until sexual maturity. Conversely, the T-receptor concentration in the hypophysis of neonatally castrated males who received TP was higher than in such animals which did not, but still lower than the level in intact adult rats; the number of hypophyseal nuclear E2-binding sites in long-term castrates which received TP was 1.5 times higher than in all the other groups of animals. The data demonstrate that in male rats sex-hormone receptors are involved in the sexual differentiation of the brain.