Immunohistochemical Localization of Inhibin Subunits in the Testis of the Bull

The differential localization of the inhibin β subunits βA and βB in the testis of adult bull was studied using specific monoclonal and polyclonal primary antibodies. Inhibin βA‐ and βB‐subunits were localized only in the Sertoli cells. The inhibin βA‐subunit was observed in the cytoplasm while the βB‐subunit was localized in the nucleus. No specific findings depending on spermatogenic stages were observed among the seminiferous tubules. Moreover, the inhibin α‐subunit was not detected in the testis of the bulls. In addition, no inhibin subunits were detected in the Leydig cells and spermatogenic cells. These findings indicate the presence of βA‐ and βB‐subunits in the bull, which may suggest a possibility that activin is produced and/or stored in the Sertoli cells and regulates spermatogenesis in an autocrine/paracrine manner. Moreover, the inhibin βB‐subunit may be produced in the nucleus but the functional meaning of this is not yet clear.