[Family of inhibins and activins: from endocrine to paracrine action]

Abstract

Inhibins and activins are structurally-related dimeric proteins mainly produced by the gonads (Sertoli cells and granulosa cells) under the stimulation of pituitary FSH. Inhibins are 32-kD glycoproteins consisting of an alpha subunit and one of two beta subunits (beta A or beta B) leading to inhibin A or B, respectively. Activins are made of two beta subunits either identical (activin A or B) or not (activin AB). These regulatory peptides are involved in an endocrine feedback loop: inhibins decrease and activins stimulate the biosynthesis and release of pituitary FSH selectively. Beside their endocrine action that has led to the discovery of these peptides, we report main experimental data showing that activins and inhibins may act as paracrine and autocrine factors within the gonads on an antagonistic mode. Inhibins and activins seem to be involved in the regulation of spermatogenesis in males and in follicular maturation in females. Potential involvements of inhibins and activins in the pathophysiology of reproduction are discussed.