ONTOGENY OF THE SENSITIZING EFFECT OF ESTRADIOL AND LUTEINIZING-HORMONE RELEASING HORMONE ON THE ANTERIOR-PITUITARY GLAND OF THE FEMALE RAT

The ontogeny of the facilitatory effect of estradiol and LHRH on the responsiveness of the anterior pituitary gland to LHRH was studied in vitro using pituitary glands from female rats aged 15, 17, 20, 31, 35 and 38 days. The facilitatory effect of estradiol was already well established by day 15, while the facilitatory effect of LHRH (priming effect) developed only after day 17. Although it increased the overall response of the gland to LHRH, estradiol did not selectively enhance the priming effect of LHRH. Both the effect of estradiol and LHRH reached a peak on day 25, 7 days before vaginal opening in this colony, and, as assessed by measuring pituitary LH [lutropin] contents, were not dependent upon the synthesis of LH. Different mechanisms may be involved in the facilitation of pituitary responsiveness by estradiol and LHRH, but both mechanisms appear to depend more upon an increase in the sensitivity of the receptor/release apparatus rather than in the gonadotropin content of the gonadotrophs.