Regulation and function of inhibins in the normal menstrual cycle.

The development of assays specific for dimeric inhibin A and inhibin B defined the distinct physiology of these two hormones in the normal menstrual cycle. Inhibin A and inhibin B expression and secretion along with their differential regulation by gonadotropins explain their unique serum patterns and their potential endocrine and ovarian autocrine-paracrine functions. There is evidence that inhibin A and inhibin B play an endocrine role in the negative regulation of follicle-stimulating hormone (FSH) in nonhuman primates and humans. However, some studies suggest that estradiol is a more important, if not the only, negative feedback regulator of FSH in women. There is also evidence from animal models that inhibins and activins play a critical role in follicle development. Future work will be necessary to define further the relative role of the inhibins, estradiol, and other autocrine-paracrine factors in these important reproductive functions.