Inhibin

Inhibin is a peptide that is an inhibitor of FSH synthesis and secretion and participates in the regulation of the menstrual cycle.

Structure

Inhibin contains an alpha and beta subunit linked by disulfide bonds. Two forms of inhibin differ in their beta subunits (A or B), while their alpha subunits are identical. Inhibin belongs to the transforming growth factor-β (TGF-β) family.

Action

FSH stimulates the secretion of inhibin from the granulosa cells of the ovary. In turn, inhibin suppresses FSH. Inhibin secretion is diminished by GnRH, and enhanced by insulin-like growth factor-I. Inhibin B reaches a peak in the early-mid follicular phase, and a second peak at ovulation, in contrast to inhibin A that reaches its peak in the midluteal phase. Inhibin is produced in the gonads, pituitary gland, placenta and other organs.

Activin

Activin is a related peptide that counteracts inhibin.