Neuroendocrine control of human ovulation

Ovulation, defined as the release of a mature oocyte from a ruptured Graafian follicle at the surface of the ovary, is the culmination of the process of follicular maturation. The latter is under the synergistic influence of the pituitary gonadotropins, follicle stimulating hormone (FSH), and luteinizing hormone (LH), the secretion of which is, in turn, stimulated by the hypothalamic decapeptide, LH-releasing hormone (LH-RH). There is a complex interrelationship between the ovarian steroid hormones, estradiol and progesterone, and the gonadotropins, with estradiol exerting both negative and positive feedback effects on the hypothalamo-pituitary unit. Ovulation is triggered by a surge of LH which results from at least two estradiol-induced phenomena, increased hypothalamic production of LH-RH and increased pituitary responsiveness to releasing hormone. Ovulation occurs 16-17 hours following the LH peak and the probability of conception following an act of coitus appears to be maximal 1-2 days prior to ovulation itself. States of anovulation are frequently seen in association with hyperprolactinemia whereas ovulation may be delayed under a variety of circumstances.