THE INHIBINS AND ACTIVINS FAMILY - FROM E NDOCRINE TO PARACRINE ACTION

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 consis ting 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 da ta showing that activins and inhibins may act as paracrine and autocri ne factors within the gonads on an antagonistic mode. Inhibins and act ivins seem to be involved in the regulation of spermatogenesis in male s and in follicular maturation in females. Potential involvements of i nhibins and activins in the pathophysiology of reproduction are discus sed.