Different roles of prepubertal and postpubertal germ cells and sertoli cells in the regulation of serum inhibin B levels

To elucidate the role of germ cells in the regulation of inhibin B secretio n, serum inhibin B levels in prepubertal boys and adult men whom had a conc urrent testicular biopsy showing either normal or impaired testicular funct ion were compared. In addition, by immunohistochemistry the cellular locali zation of the two subunits of inhibin B (alpha and beta B) were examined in adult testicular tissue with normal spermatogenesis, spermatogenic arrest, or Sertoli cell only tubules (SCO) as well as in normal testicular tissue from an infant and a prepubertal boy. Adult men with testicular biopsy show ing normal spermatogenesis (n = 8) or spermatogenic arrest (n = 5) had medi an inhibin B levels of 148 pg/mL (range, 37-463 pg/mL) and 68 pg/mL (range, 29-186 pg/mL), respectively, corresponding to normal or near-normal levels of our reference population (165 and 31-443 pg/mL; n = 358). Men with SCO (n = 9) had undetectable or barely detectable (n = 1) serum levels of inhib in B. In contrast to adults, prepubertal boys with SCO (n = 12) all had mea surable serum inhibin B levels that corresponded to our previously determin ed normal range in healthy prepubertal boys (n = 114). However, in postpube rtal samples from the same SCO boys, inhibin B levels were undetectable as in the adult SCO men. Intense inhibin alpha-subunit immunostaining was evid ent in Sertoli cells in both prepubertal and adult testes. In the prepubert al testis, positive immunostaining for the beta B-subunit was observed in S ertoli cells. In the adult testis, intense immunostaining for the beta B-su bunit was evident in germ cells from the pachytene spermatocyte to early sp ermatid stages and to a lesser degree in Leydig cells, but not in Sertoli c ells or other stages of germ cells. Thus, surprisingly, in adult men the tw o subunits constituting inhibin B were expressed by different cell types. W e speculate that during puberty Sertoli cell maturation induces a change in inhibin subunit expression. Thus, immature Sertoli cells express both alph a and beta B inhibin subunits, whereas fully differentiated Sertoli cells o nly express the alpha-subunit. The correlation in adult men between serum i nhibin B levels and spermatogenesis may be due to the fact that inhibin B i n adult men is possibly a joint product of Sertoli cells and germ cells, in cluding the stages from pachytene spermatocytes to early spermatids.