Follistatin and activin A production by the male reproductive tract

Follistatin is a binding protein for the activin and inhibin family of horm ones, regulating their biological activity. In the male reproductive tract, the interaction of these factors is likely to be involved in the regulatio n of the proliferation of several cell types. We have investigated the pres ence of follistatin and activin A in seminal plasma using specific immunoas says and have localized follistatin and activin/inhibin subunits in the adu lt human testis, prostate and seminal vesicle to establish their likely sou rces. High concentrations of immunoreactive follistatin were present in sem inal plasma in normal men (mean 97.9 ng/ml; 1.43 ng/ml in peripheral plasma ) and were similar in men with oligo/azoospermia and following vasectomy, F ollistatin immunoreactivity was localized to both Leydig and Sertoli cells of the testis, and to epithelial cells of the prostate gland and seminal ve sicle, which are likely to be the predominant sources of the hormone in sem inal plasma. Activin A was also present in seminal plasma in normal men but was undetectable following vasectomy, thus deriving from the testis. Consi stent with this finding, the PA-subunit was immunolocalized in Sertoli and Leydig cells but was not present in seminal vesicle or prostate gland. The functional significance of the high concentrations of follistatin secreted into seminal plasma by the prostate gland and/or seminal vesicle is uncerta in, but they may regulate the biological activity of testis-derived activin A and inhibin B.