The corpus luteum of the primate menstrual cycle is capable of recovering from a transient withdrawal of pituitary gonadotropin support

Abstract

To further our understanding of the role of pituitary gonadotropin secretion in the control of corpus luteum function during the primate menstrual cycle, we have used an experimental model which enables us to directly control pituitary gonadotropin secretion throughout the luteal phase. Specifically, we have asked whether cessation of progesterone secretion, or functional luteolysis, resulting from a 3–day withdrawal of gonadotropin support, culminates in an irreversible loss of luteal responsiveness to further gonadotropic stimulation; and do the effects of gonadotropin deprivation vary with the age of the corpus luteum? Endogenous gonadotropin secretion was abolished in seven adult rhesus monkeys by placing radiofrequency lesions in the arcuate nucleus region of the medial basal hypothalamus. Endogenous gonadotropin secretion and ovulatory menstrual cycles were then restored by chronic pulsatile infusion of GnRH (1 pulse/h). Control luteal phases supported by this GnRH regimen exhibited typical plasma progesterone patterns and ranged from 14–17 days in length. In experimental cycles, endogenous gonadotropin secretion was interrupted for a 3-day period during the early (days 2–5), mid (days 8–11), or late (days 13–16) stages of the luteal phase. During the GnRH deprivation period, bioassayable and immunoreactive serum LH was undetectable. The disappearance of circulating LH was followed by a rapid fall in plasma progesterone levels regardless of the stage of the luteal phase. The restoration of gonadotropin secretion resulted in a resumption of progesterone secretion when the gonadotropin deprivation period was imposed during the early or midluteal phase. In each instance, the resumption of progesterone secretion continued for a period of time which effectively completed the typical 14– to 17–day functional lifespan of the corpus luteum of the menstrual cycle. Thus, the luteal phase was neither shortened nor lengthened by a 3–day interruption of luteal function resulting from withdrawal of gonadotropic support. When gonadotropin secretion was interrupted during the late luteal phase (days 13–16), restoration of gonadotropin secretion on day 16 did not result in resumption of progesterone secretion. Our findings confirm our earlier demonstration that progesterone secretion during the luteal phase of the nonfertile menstrual cycle is dependent on pituitary gonadotropic support. Whereas progesterone secretion is dependent on pituitary gonadotropin, the maintenance of the capacity of the corpus luteum (maintenance of steroidogenic enzymes) is less dependent on, or perhaps independent of, gonadotropic support. The corpus luteum of the menstrual cycle can recover from transient withdrawal of gonadotropic support which results in functional luteolysis, but the degree to which luteal function is restored varies with the age of the corpus luteum. © 1985 by The Endocrine Society.