Perspectives in Biology and Medicine

THE POSSIBLE VASCULAR REGULATION OF LUTEAL FUNCTION BRUCE B. PHARRISS, Ph.D.* Thecorpusluteum is one ofthemost uniquestructures that exist inmammals . This endocrine gland appears out of"primordiallike" cells, grows to maturity, and then completely disappears, at least functionally. All this occurs in a period quite limited when compared with the functional life ofthe ovary itself. The fleeting quality ofthe gland has been commented upon by Rothchild [i]: "This ephemerality is one of the most distinctive features ofthe corpus luteum and may be a clue to the nature ofits activity and the way this activity is regulated." The manner in which the corpus luteum is regulated has intrigued reproductive physiologists for several decades (fig. i). The role ofthe hypothalamus has been described at length, as have several routes for feedback control ofgonadotropin release originating from the ovary. It is generally accepted that the anterior pituitary is controlled by releasing factors or inhibiting factors which are liberated from various centers in the hypothalamus and reach the pituitary by way of the specialized portal blood system connecting these two areas. Each pituitary gonadotropin has its hypothalamic factor—a releasing factor for follicle stimulating hormone (FSH) and luteinizing hormone (LH) each and an inhibiting factor for prolactin, at least in the rat. The FSH released is thought to be responsible for follicular maturation and estrogen secretion. The LH induces ovulation and luteinization of the granulosa cells which undergo hypertrophy and hyperplasia until the mature corpus luteum is formed. This corpus luteum is the source of progesterone. The estrogens and progestogens, besides priming the uterus for reproductive processes, also feed back on the hypothalamus and pituitary to regulate gonadotropin release. It is also known * Research associate, Fertility Research, Upjohn Company, Kalamazoo, Michigan 49001. I wish to thank L.J. Wyngarden, G. D. Gutknecht, andJ. C. Cornette for their invaluable technical assistance in this work. 434 Bruce B. Pharriss · Luteal Function Perspectives in Biology and Medicine · Spring 1970 that both steroid hormones (when administered in pharmacologic doses) can inhibit LH and FSH release, but data for some species imply that correct levels circulating at the correct time may be the stimulus for gonadotropin release. The big question is:What brings this cycle to a close? As long as the corpus luteum is active and secreting progesterone, a new cycle cannot hypothalamus RELEASING FACTORS fr ANTERIOR PITUITARY F.S.H. L.H.PROLACTIN Progesterone Secretion from CORPUS LUTEUM Ovulation, Malntonanco of CORPUS LUTEUM Maturation estrogen Secretion from FOLLICLE Formation of CORPUS FOLLICLE¦¿3SL