Effects of Ergocornine on Serum Prolactin and LH, and on Hypothalamic Content of PIF and LRF

Abstract

Daily injections of 400 jug ergocornine/100 g bw for 20 days or a single implantation of approximately 200 μg in the median eminence suppressed all fluctuations in serum prolactin values during the estrous cycle and depressed pituitary prolactin and LH levels in rats. Regularity of estrous cycles was not disturbed as determined by daily vaginal smears. An injection of 5, 50, or 200 μg of ergocornine/100 g bw in the early afternoon of proestrus completely prevented the marked rise in serum prolactin which normally occurs on the late afternoon of proestrus. Only doses of 50 or 200 μg of ergocornine significantly depressed the normal serum LH peak on the late afternoon of proestrus. All animals ovulated during the following night, suggesting that less LH is required to induce ovulation than is normally released by the pituitary. Male pituitary halves incubated in vitro with hypothalamic extract from ergocornine-treated animals released less prolactin and LH than the corresponding pituitary halves incubated with hypothalamic extract from rats, indicating that hypothalamic PIF was increased and LRF was decreased. Although this suggests that ergocornine acts via the hypothalamus to depress pituitary secretion of prolactin and LH, the possibility of a direct action of the drug on the pituitary cannot be excluded. (Endocrinology88: 737, 1971)