Steroids and pituitary responsiveness in female, androgenized female and male rats

Spontaneous gonadotrophin release and the gonadotrophin response to LH releasing factor (RF) were studied in pro-oestrus, androgenized female and male rats. The animals were either intact or gonadectomized (about 32 h previously) and treated with various steroids. The gonadotrophin response (especially LH) was much lower in intact males and androgenized females than in pro-oestrous females. Oestrogen plus progesterone increased plasma gonadotrophin concentrations and responses in ovariectomized rats, but inhibited the increase in the plasma gonadotrophin concentration and the LH response which followed castration in males. As in the normal female, ovariectomy decreased the LH response but increased the plasma FSH concentration and response in the androgenized female; oestrogen and progesterone had relatively little effect. Apart from reducing the postcastration rise in plasma FSH, testosterone had no significant effect in gonadectomized male or female animals. These results show that the effect of steroids on the gonadotrophin response to LH-RF as well as the spontaneous secretion of gonadotrophin depends upon sexual differentiation of the hypothalamo-hypophysial system. Studies with various metabolites of progesterone indicated that the facilitatory action of this steroid could be due, in part, to a 5alpha-reduced derivative.