Which hormone binds to activin, blocking its action?

Follistatin plays a crucial role in reproductive physiology by acting as a binding protein to activin, a member of the transforming growth factor-beta superfamily. Activin is involved in various biological processes such as regulating the menstrual cycle, follicle-stimulating hormone (FSH) production, and promoting the growth and development of ovarian follicles. When follistatin binds to activin, it effectively inhibits activin's biological activity, thereby modulating its effects on the reproductive system.

This inhibition is significant in maintaining the delicate hormonal balance within the body, especially in the context of ovarian function and fertility. By blocking activin's action, follistatin helps to prevent an overproduction of FSH and supports normal reproductive processes. This function of follistatin is essential for ensuring appropriate responses during the menstrual cycle and in the broader context of reproductive health.