Different Roles of Prepubertal and Postpubertal Germ Cells and Sertoli Cells in the Regulation of Serum Inhibin B Levels1

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Abstract
To elucidate the role of germ cells in the regulation of inhibin B secretion, serum inhibin B levels in prepubertal boys and adult men whom had a concurrent testicular biopsy showing either normal or impaired testicular function were compared. In addition, by immunohistochemistry the cellular localization of the two subunits of inhibin B (α and βB) 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 showing normal spermatogenesis (n = 8) or spermatogenic arrest (n = 5) had median 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 inhibin B. In contrast to adults, prepubertal boys with SCO (n = 12) all had measurable serum inhibin B levels that corresponded to our previously determined normal range in healthy prepubertal boys (n = 114). However, in postpubertal samples from the same SCO boys, inhibin B levels were undetectable as in the adult SCO men. Intense inhibin α-subunit immunostaining was evident in Sertoli cells in both prepubertal and adult testes. In the prepubertal testis, positive immunostaining for the βB-subunit was observed in Sertoli cells. In the adult testis, intense immunostaining for the βB-subunit was evident in germ cells from the pachytene spermatocyte to early spermatid stages and to a lesser degree in Leydig cells, but not in Sertoli cells or other stages of germ cells. Thus, surprisingly, in adult men the two subunits constituting inhibin B were expressed by different cell types. We speculate that during puberty Sertoli cell maturation induces a change in inhibin subunit expression. Thus, immature Sertoli cells express both α and βB inhibin subunits, whereas fully differentiated Sertoli cells only express the α-subunit. The correlation in adult men between serum inhibin B levels and spermatogenesis may be due to the fact that inhibin B in adult men is possibly a joint product of Sertoli cells and germ cells, including the stages from pachytene spermatocytes to early spermatids.