Local extragonadal roles of activins.

Activins were initially isolated from gonadal fluids based on their ability to stimulate FSH secretion from gonadotropes of the anterior pituitary. They represent a group of homo/heterodimeric proteins that are structurally related to the transforming growth factor beta superfamily of growth and differentiation factors. The importance of activins as autocrine and paracrine modulators of a diverse set of biologic functions is now appreciated based on their widespread anatomic distribution and numerous biologic activities.