Gonadotoropin actions on spermatogenesis and hormonal therapies for spermatogenic disorders [Review].

Microdissection testicular sperm extraction and intracytoplasmic sperm injection have made it possible for men with non-obstructive azoospermia (NOA) to conceive a child. A majority of men cannot produce sperm because spermatogenesis per se is believed to be "irreversibly" disturbed. For these men, it has been thought that any hormonal therapy will be ineffective. Further understandings of endocrinological regulation of spermatogenesis are needed and LH or FSH receptor knock out (KO) mice have revealed the roles of gonadotropin separately. Spermatogenesis has been shown to shift during evolution from FSH to LH dominance because LH receptor KO causes infertility while FSH receptor KO does not. High concentrations of intratesticular testosterone secreted from Leydig cells, ranging from 100- to 1,000-fold higher than in the systemic circulation, has pivotal roles during spermatogenesis. This is especially important during spermiogenesis, a post-meiotic step for progression from round to elongating spermatids. Sertoli cells are the target of FSH and have numerous androgen receptors, indicating that Sertoli cells are regulated by FSH and the paracrine functions of testosterone. In combination with Leydig cell-derived growth factors, particularly epidermal growth factor-like growth factors, Sertoli cells support spermatogenesis, especially at proximal levels of spermatogenesis (e.g., spermatogonial proliferation). Taken together, the current knowledge from human studies indicating that testosterone optimization by clomiphene, hCG and/or aromatase inhibitors and high dose hCG/FSH treatment can, at least in part, improve spermatogenesis in NOA. Accordingly hormonal therapy may open a therapeutic window for sperm production in selected patients.