Immunodetection of inhibin in the human testis and epididymis during normal development and in non-tumoural testicular lesions.

Plasma concentrations of inhibin are correlated with spermatogenetic function. Inhibin is secreted mainly by the Sertoli and Leydig cells of the testis. In the human epididymis, the location and function of inhibin are contentious. Thus, the aim of the present study was to determine the location of inhibin in the human epididymis. Investigations were performed in samples with normal testicular function at different stages of development, as well as in samples in which testicular function or the testicular-epididymal connection were altered. In fetal, newborn and infant testes, Sertoli and Leydig cells stained positive for inhibin, whereas no such staining was detected in the epididymides. Inhibin was located in both the Sertoli and Leydig cells, as well as in the epididymis, in the apical pole of mainly secretory cells in the efferent ducts. This staining pattern was not correlated with the staining pattern for macrophages. The main duct of the epididymis was negative for inhibin staining. In ischaemic atrophic testes, the few tubules in which Sertoli cells were present stained positive for inhibin, whereas the epididymides stained negative. In paediatric cryptorchidism, Sertoli and Leydig cells stained positive for inhibin, whereas the epididymides were negative. In adult cryptorchidism, Sertoli and Leydig cells stained positive for inhibin, even in tubules containing Sertoli cells only. Interestingly, inhibin was absent from the efferent ducts. In three cases undergoing hormonal treatment prior to subsequent gender change, Sertoli and Leydig cells stained positive for inhibin. In contrast, the efferent ducts were negative or only faintly positive in cases of shorter hormonal treatment. In all cases studied, the presence of inhibin in the efferent ducts was associated with its production in the testis, suggesting that the epididymis is not responsible for the production of inhibin in men. The pattern of inhibin staining does not correlate with that of macrophages, suggesting that inhibin is not degraded in the human epididymis. The data suggest that, in humans, inhibin is secreted by Sertoli cells into the seminiferous tubules and then travels towards the efferent ducts, where it is reabsorbed into the bloodstream.