Inhibin B
Hormonal / ReproductiveAlso known as: Inhibin-B, Inhibin Beta-B, INHB
Mechanism
Inhibin B is a hormone produced by the testes (Sertoli cells) in men and the ovaries in women. Its main job is to put the brakes on FSH secretion from the pituitary, providing negative feedback in the reproductive axis. In men, inhibin B levels serve as a marker of spermatogenesis and Sertoli cell function. In women, it is a marker of ovarian reserve and follicular activity.
Technical detail
Inhibin B is a heterodimeric glycoprotein of the TGF-beta superfamily, composed of an alpha subunit (INHA) disulfide-linked to a betaB subunit (INHBB). It acts primarily on anterior pituitary gonadotrophs to selectively suppress FSH synthesis and secretion by antagonizing activin signaling. Mechanistically, inhibin binds betaglycan (TGF-beta receptor III) as a co-receptor, then forms a complex with ActRII to competitively block activin-mediated Smad2/3 signaling. In males, it is produced by Sertoli cells and reflects spermatogenic function. In females, granulosa cells of small antral follicles are the primary source.