Abstract

PIP: The current knowledge of the influence of gonadotropins on ovarian function is reviewed based primarily on human data but supplemented with references to animal studies. 2 aspects of ovarian function are under the influence of gonadotropins--follicular growth and maturation and steroid synthesis and secretion. Follicular stimulatin hormone (FSH) promotes the growth of more advanced follicles. Recent evidence suggests that estrogens increase the capacity of the ovary to bind FSH. There is evidence that estrogen is produced in the theca interna of the maturing follicle. It seems likely that the ultrastructural, enzymatic, and secretory changes seen in the thecae result from stimulation by low tonic levels of plasma luteinizing hormone (LH) in combination with FSH. At ovulation the surge of gonadotropins is triggered off by the ri sing estrogen output. Graafian follicles respond to LH in vitro with increased synthesis of progesterone and lactic acid. The capacity to lutenize spontaneously develops before ovulation and perhaps the oocyte inhibits this function. The development of the human corpus luteum is summariezed and the pattern of progesterone production described. LH and human chorionic gondtropin acutely stimulate steroid synthesis by binding to specific sites on luteal cell menbranes to increase the synthesis of cyclic AMP. The corpus luteum of early pregnancy differs morphologically and functionally from that of the cycle, increasing progesterone production which remains high until the 11th or 12th week of pregnancy. The cortical stroma of the human ovary is steroidogenic i n character but producing androstenedion. The stroma's capacity for synthesis varies with the cycle stage. Each cell type synthesizes its characteristic spectum of steroid products. How appropriate enzymes become activated in the cell and thus produce these steroids is as yet unknown. Gonadotropins only initiate this differentiation and subsequently enhance the activity of transformed cells.