Testosterone replacement therapy and spermatogenesis in reproductive age men.

Testosterone has a pivotal role in spermatogenesis, erectile function, libido and expression of secondary sexual characteristics. The prevalence of symptomatic, laboratory-proven testosterone deficiency increases with age and is often treated with testosterone replacement therapy (TRT). Treatment with exogenous androgens suppresses gonadotropin levels, inhibits endogenous testosterone production and drastically reduces intratesticular testosterone, consequently impairing spermatogenesis. Sperm production often slowly resumes after TRT cessation. However, the rate of recovery shows highly variable kinetics that might complicate family planning. Medical therapies (including aromatase inhibitors and selective oestrogen receptor antagonists) and exogenous gonadotropins (including human chorionic gonadotropin and follicle-stimulating hormone) may be used to preserve or restore spermatogenesis in select populations receiving TRT. Exogenous testosterone is contraindicated in men trying to conceive, but new short-acting formulations, including oral testosterone undecanoate and nasal testosterone gel, might incompletely suppress the hypothalamic-pituitary-gonadal axis and partially preserve spermatogenesis.