Inhibins, activins and follistatin: actions on the testis

While the early Studies of the inhibins, activins and follistatins concentr ated on their role as endocrine regulators of FSH secretion, recent data ha s emphasized the local actions of the activins and follistatin. Inhibin. th rough its capacity to suppress FSH secretion can modulate numerous processe s within the testis. However, to date, evidence to support a local role for inhibin is limited. In contrast, activin and its binding protein follistat in are produced by a large number of cell-types within the testis raising t he possibility of a range of paracrine and autocrine actions. These include the modulation of androgen production, influence on the proliferation of S ertoli cells and germ cells as well as the capacity to influence the struct ural and functional features of mitochondria within germ cells. Some of the se actions are carefully controlled in a temporal relationship during the d evelopment of testicular function in the rat in which there is no separatio n in time between birth and the onset of spermatogenesis. Given the range o f actions of activin in different cell-types, recognition of systems that a re designed to modulate its actions are crucial in enhancing our understand ing of how these many roles can be compartmentalized. (C) 2001 Elsevier Sci ence Ireland Ltd. All rights reserved.