The testis has two functions, androgen production and spermatogenesis, and a key role in their regulation is played by the two pituitary gonadotropins, luteinizing hormone and follicle-stimulating hormone (FSH). Other hormones and growth factors also influence testicular function, often by modulating the gonadotropin effects. Moreover, a plethora of local paracrine and autocrine signals within the testis are known. The main testicular hormone, testosterone, a Leydig cell product, regulates spermatogenesis in seminiferous tubules in paracrine fashion. The other functions of testosterone are endocrine, occurring outside the testis.
This chapter summarizes the main hormonal regulatory system of the testis, the hypothalamic–pituitary–testicular axis, and how its effects are modulated by other extratesticular hormones and local testicular factors.