Estradiol positive feedback on the rat anterior pituitary gland in vitro

LH surges can be elicited by estradiol (E2). The mechanism could be either by induction of a surge of hypothalamic LH-RH or by directly increasing the responsiveness of the pituitary gland to hypothalamic LH-RH without an LH-RH surge. In order to study the positive feedback of E2 on the anterior pituitary gland, without any possible influence of an LH-RH surge, we utilized long-term in vitro superfusion of the anterior pituitary gland. The E2 concentration was 100 pg/ml and 10(-8) M LH-RH was pulsed every 30 min for 3 min. LH and FSH surge was detected about 21 h after the beginning of the E2 infusion in all three repeated experiments. No surge was detected in any other channels, i.e. control, E2 superfusion alone or LH-RH stimulation alone. This study demonstrates that in the rat the induction of the preovulatory LH peak can be accomplished by a direct effect of E2 upon the anterior pituitary gland, provided it is being stimulated by constant pulses of LH-RH.