Discussion
Testis, testis
TESTIS, STILL
This study shows that low serum AMH is a marker for poor gonadal function illustrated by impaired semen quality and lower serum inhibin B, inhibin B/FSH ratio, testosterone/LH ratio, and higher serum FSH in a well-characterized cohort of infertile men. AMH is produced by Sertoli cells, but its biological function in postnatal life is largely unknown. This study suggests that low serum AMH may reflect a poor Sertoli cell function, which is supported by the lower serum inhibin B, higher FSH, and lower inhibin/FSH ratio in men having the lowest serum AMH with a threshold at 26 pmol/L. The observed low inhibin B/FSH ratio and impaired semen quality in men with the lowest serum AMH suggest that low AMH reflects inappropriate Sertoli cell function, which may be unable to support an adequate number of germ cells. This suggestion is supported by the concomitant threefold lower sperm quantity and smaller testis size in men with low serum AMH. Testis size is largely determined by the number of germ cells, which indicates that low serum AMH may be a marker of the function of seminiferous tubules and Sertoli-germ cell interaction. Still, low AMH may also reflect Leydig cell function although serum testosterone, estradiol, and LH were not different between men stratified according to AMH tertiles. Instead, the testosterone/LH ratio was lower, which suggests that men with low AMH in addition to impaired Sertoli cell function may have impaired Leydig cell function.Ideally, the observed differences in reproductive hormones between AMH groups could be supported by evaluation of testis histology, but despite this limitation, it is unlikely that men with low serum AMH have more immature Sertoli cells as they in theory would produce higher levels of AMH than mature Sertoli cells [Serum inhibin B and FSH were also associated with sperm production, and serum FSH was stronger associated with sperm production compared with serum AMH and serum inhibin B. FSH is known to be a potent regulator of sperm production in both mice and humans. However, the association between serum AMH and sperm production was not inferior to the link found with serum inhibin B and sperm production. Furthermore, serum AMH was strongly associated with serum inhibin B and serum FSH, which are in line with previous studies [In vitro data indicate a regulatory role of vitamin D for AMH production [We propose that serum AMH in infertile men is a marker for Sertoli cell health and function that ultimately, may be used to select the infertile men who will benefit from a Sertoli cell stimulator such as FSH, clomiphene or as recently suggested a receptor activator of nuclear factor kappa-β ligand (RANKL) inhibitor [