Gonadal peptides: Inhibins, activins, follistatin, and Müllerian-inhibiting substance (Antimüllerian hormone)

Activins A and B both stimulate FSH secretion, and this and their other actions are modulated by follistatin, a protein that binds the activins virtually irreversibly and thus decreases FSH.- Activin A is a key regulator of the inflammatory response and stimulates fibrosis, and follistatin is thus an antiinflammatory and antifibrotic agent.- Elevated levels of activin A stimulate apoptosis of hepatocytes and B lymphocytes, actions that are all decreased by follistatin.- Follistatin also binds and decreases the actions of other TGF-β proteins, myostatin (GDF8), GDF9, and BMPs 2, 5, 7, and 8.- Mullerian inhibiting substance may be of value as a marker of ovarian follicle reserve and is claimed to assist in predicting the ovarian response to gonadotropin stimulation, a concept requiring further confirmation.