INHIBINS, ACTIVINS, THEIR BINDING-PROTEINS AND RECEPTORS - INTERACTIONS UNDERLYING PARACRINE ACTIVITY IN THE TESTIS

The inhibin-related peptides are present in the testis from early gest ation through adulthood. They are produced from multiple testicular si tes in a highlyregulated manner, suggesting important paracrine roles. Similarly, receptors for these peptides are located in specific stage s of the seminiferous tubule and on particular cell types, and an addi tional level of control is afforded byspecific binding proteins, such as follistatin, which may regulate bioavailability. The actions of the se factors include the modulation of interstitial cell function and th e increase of spermatogonial proliferation in vitro. It thus appears t hat activin and inhibin are significant factors in the local control o f testicular funtion.