Inhibin is a protein secreted by granulosa (female) and Sertoli (male) cells in response to FSH, and its major action is the negative feedback control of pituitary FSH secretion. It is found in blood plasma, although difficult to detect until recently. Inhibin is produced in the gonads, pituitary gland, placenta, corpus luteum and other organs. Inhibin does not inhibit the secretion of GnRH from the hypothalamus