INHIBIN : A NEW BIOLOGICAL MARKER IN OVARIAN CANCER

Abstract

Inhibin, a member of the TGF-superfamily, is a heterodimer glycoprotein gonadal hormone. There are two types of inhibin, inhibin A and B, which have apparently identical biological activity. Both inhibins have structurally similar a subunits linked by disulphide links to structurally different subunits CPA in inhibin A, and B in inhibin B). Inhibins are found in the circulation as monomers or dimers of different molecular weight forms dille to processing of the precursors at different sites before and after dimerization. The mature dimeric inhibin form of 32 Kd is regarded as the biologically active form. Although inhibin is found in different tissues such as adrenal gland, prostate, endometrium, fetal membranes, gastric mucosa, breast, brain, spleen, pituitary gland and bone marrow, the main source of inhibin is the granulosa cells of the ovary in females and the Sertoli and Leydig cells of the testis in males, with the exception of pregnancy when the placenta becomes the major source of inhibin. Inhibin was originally defined as a gonadal hormone which inhibits FSH secretion from anterior pituitary. FSH. and LH stimulate inhibin secretion in males and females, which in tum on increasing inhibit FSH secretion without affecting LH release. In contrast, decreased inhibin levels stimulate FSH secretion. Serum inhibin levels vary according to age, sex and physiological conditions. Inhibin B is the likely active form in males and early in the menstrual cycle in females, while inhibin A is increased late in the menstrual cycle and pregnancy.