James S. Hutchison

Luteotropic Actions of LH on the Macaque Corpus Luteum

The primate corpus luteum of the menstrual cycle secretes progesterone for 14–16 days after ovulation in the absence of an implanted conceptus (1). In fertile cycles, the luteal life span is prolonged by the secretion of chorionic gonadotropin by the trophoblast (2). In view of its absolute requirement for implantation and early gestation, specific knowledge of the regulation of the corpus luteum is important for effective control of fertility as well as correcting the pathophysiological conditions of short and inadequate luteal phases.

On the Site of Action of Progesterone in the Blockade of the Estradiol-induced Gonadotropin Discharge in the Rhesus Monkey

The site of action of progesterone (P) in the blockade of estradiol-induced gonadotropin discharges was examined in rhesus monkeys bearing hypothalamic lesions which abolish endogenous GnRH production. Normal ovulatory menstrual cycles were re-established in these animals by the pulsatile, hourly administration of GnRH. In the follicular phase of these induced menstrual cycles, P-containing Silastic capsules were implanted sc yielding luteal phase plasma P concentrations which normally block estradiol-induced gonadotropin surges. P failed to block estradiol-induced surges in lesioned animals on GnRH replacement. In such animals, however, P advanced the initiation of these surges. While estradiol acts on the pituitary to cause gonadotropin discharges, P appears to block this effect by acting on the central nervous system. On the other hand, the results also suggest that the site of facilitatory action of P on gonadotropin release is at the level of the pituitary gland.