DOES INHIBIN HAVE AN ENDOCRINE FUNCTION DURING THE MENSTRUAL-CYCLE

Inhibin (alpha-beta heterodimer) has been considered to be the principal non-steroidal ovarian regulator of pituitary FSH secretion. The beta-beta heterodimer, activin, produced by the ovary and other tissues, appears to act locally, with actions opposite to those of inhibin. Since immunoreactive inhibin is highest during the luteal phase of the menstrual cycle when FSH is lowest, a negative feedback role in controlling FSH release at this time has been suggested Attempts to establish this by using immunoneutralization techniques have failed to reveal such a role. We must enhance our understanding of the gonadotropic control of inhibin/activin gene expression within the various compartments of the primate ovary, the role of their binding proteins, and the nature of the secretory products before we can resolve the question of whether inhibin has an endocrine function during the menstrual cycle and how cyclic reinitiation of follicular development is controlled.