Serum inhibin B levels during male childhood and puberty.

Inhibin B is a testicular peptide hormone that regulates FSH secretion in a negative feedback loop. In males serum levels of inhibin B are detectable throughout life with prominent changes in the first year of life and during puberty. Serum inhibin B is normally detectable throughout childhood where it is a direct marker of the presence and function of Sertoli cells. The inhibin B analysis has proven useful in the diagnosis of patients with non-palpable testes. Undetectable or low inhibin B levels are observed in boys with either congenital or acquired absence of testicular tissue whereas normal or near-normal levels are seen in cryptorchidism and disorders with preserved Sertoli cell function in spite of absence of germ cells or impaired androgen biosynthesis or action. During puberty a developmental change in the regulation of serum inhibin B occurs. In contrast to childhood inhibin B levels, inhibin B production in adult men is dependent on the presence of certain germ cells in the seminiferous tubules, most likely involving the pachytene spermatocytes and early spermatids. Thus, in adult men serum inhibin B levels are closely related to spermatogenesis with undetectable or low levels observed in SCO syndrome and early stage spermatogenic arrest whereas normal or near normal levels are observed in men with late stage spermatogenic arrest or obstructive forms of azoospermia. These clinical findings are in accordance with immuno-histological studies of the expression of inhibin B subunits in human testis.