Inhibin: Regulation of reproductive function and practical use in females

Inhibins are gonadal glycoprotein hormones selectively and potently inhibiting follicle‐stimulating hormone (FSH) secretion from the pituitary gland. Inhibins are produced mainly by the ovary and are purified from follicular fluid. Inhibins were shown to be produced in two forms through dimeric assembly of an α‐subunit and one of two closely related β‐subunits to form inhibin A (α‐βA) and inhibin B (α‐βB). Although inhibin subunits are expressed in various tissues, the gonads are the major source of circulating inhibins. While inhibins may act as a paracrine or autocrine factor in some tissues, their best understood roles are as endocrine regulators of pituitary FSH. In this review we focus our attention on more recent developments in inhibin research. We describe patterns of inhibin A and B secretion during the estrous cycle. We also review the immunization against inhibin α subunit as a practical method for superovulation. Superovulation has been induced successfully by passive or active immunization against the inhibin α‐subunit in several species such as mice, rats, hamsters, guinea pigs, cows, mares, ewes and goats. Furthermore, several studies have shown that oocytes superovulated with immunization against inhibin α‐subunit have the ability to develop normally, suggesting that inhibin immunization could be used as a practical method for superovulation in a wide range of animal species.