[New model of the endocrine regulation of the female menstrual cycle]

Recent studies have modified remarkably our concepts regarding the hormonal control of the human menstrual cycle. The previously accepted hypothesis was mainly based on rat experiments. It postulated a single integrated hypothalamic-pituitary-ovarian feedback system directed by a "CNS clock". Primate investigations now suggest two interrelated, but separable functional elements, i.e. a hypothalamic-pituitary unit and a gonadal-pituitary unit. The continuous pulsatile, yet unvarying hypothalamic secretion of gonadotropin-releasing hormone (GnRH) facilitates a direct pituitary response to changing estrogen levels. Thus, GnRH plays only a permissive, albeit obligatory role, while an "ovarian clock" provides the critical signal for the cyclic surge of LH and FSH. "Physiological" substitution of exogenous GnRH may be used to treat gonadal dysfunction in women and men which is caused by pathologic changes of the amplitude and/or frequency of hypothalamic GnRH secretion. "Pharmacodynamic" administration of potent GnRH analogues promises to become an effective and safe method of contraception as well as a new approach in the treatment of endometrium and other estrogen-dependent dysfunctions.