Follistatin and activin A production by the male reproductive tract

Follistatin is a binding protein for the activin and inhibin family ofhormones, regulating their biological activity. In the male reproductivetract, the interaction of these factors is likely to be involved in theregulation of the proliferation of several cell types. We have investigatedthe presence of follistatin and activin A in seminal plasma using specificimmunoassays and have localized follistatin and activin/inhibin subunits inthe adult human testis, prostate and seminal vesicle to establish theirlikely sources. High concentrations of immunoreactive follistatin werepresent in seminal plasma in normal men (mean 97.9 ng/ml; 1.43 ng/ml inperipheral plasma) and were similar in men with oligo/azoospermia andfollowing vasectomy. Follistatin immunoreactivity was localized to bothLeydig and Sertoli cells of the testis, and to epithelial cells of theprostate gland and seminal vesicle, which are likely to be the predominantsources of the hormone in seminal plasma. Activin A was also present inseminal plasma in normal men but was undetectable following vasectomy, thusderiving from the testis. Consistent with this finding, the betaA-subunitwas immunolocalized in Sertoli and Leydig cells but was not present inseminal vesicle or prostate gland. The functional significance of the highconcentrations of follistatin secreted into seminal plasma by the prostategland and/or seminal vesicle is uncertain, but they may regulate thebiological activity of testis-derived activin A and inhibin B.