Endocrinology of the Testis and Male Reproduction by Manuela Simoni & Ilpo T. Huhtaniemi

Author:Manuela Simoni & Ilpo T. Huhtaniemi
Language: eng
Format: epub
Publisher: Springer International Publishing, Cham

Idiopathic azoospermia or oligozoospermia

Classification of HG by Age of Onset

As it is implied in many of the aforementioned disorders, the time of onset of gonadal failure may sometimes be more important for the clinical presentation of HG than the localization of the cause per se. An explanation for this fact may be retrieved by a brief description of the stages of the ontogenesis of the male genitalia and the development of male sexual characteristics.

Regardless of the karyotype of an individual, male gonadal sex is determined by the presence or absence of the SRY gene, which is normally located at the short arm of the Y chromosome. The secretion of AMH by the Sertoli cells that reside only in the male gonad triggers the regression of Müllerian ducts and their derivatives (fallopian tubes, uterus, and the upper third of the vagina). Leydig cells, initially driven by placental hCG and later by fetal LH, secrete T and INSL-3, which are responsible for the stabilization of the Wolffian tube derivatives (seminiferous ducts), the virilization of the external genitalia and the descent of the testicles in the scrotum.

In neonates, the HPT axis is activated temporarily from the first week of life and may remain active for 3–6 months after birth as a result of elimination of the maternal high estrogen milieu at birth, a period also known as “mini puberty” (Cohn et al. 1993). Interestingly, elevated T cannot induce meiosis and promote spermatogenesis at this stage, most probably due to the lack of AR expression on Sertoli cells. Later in infancy and childhood, a long period of quiescence ensues while androgen production is negligible; Sertoli cells, however, remain active and secrete AMH, preparing the testis for the forthcoming awakening at puberty. In puberty, the HPT axis is reactivated increasing T secretion from the testes, an event which coincides with AR expression on Sertoli cells and triggers the first wave of spermatogenesis. T soon thereafter reaches adult concentrations, inducing sexual maturation and achievement of adult body proportions.

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