Abstract: Testis as male gonad produces sperm and androgen. Sperm is produced in the seminiferous tubule, while androgen in the interstitial cells (Leydig cells). Androgen plays important roles in male sexual differentiation, pubertal development, second sexual characteristics and maturation, and male fertility. Androgen production in Leydig cells is controlled by the hypothalamus-hypophysis-testis axis, through the LH-LHR-cAMP-PKA pathway. In fact, the intratesticular regulation, including paracrine, autocrine and intracellular secretion, is very important for regulating androgen production. Many intratesticular factors, such as prolactin, insulin, IGF-1, TGF-α and TGF-β, have been well expounded. Besides cAMP, Ca2+ is another important second messenger. It was found that calmodulin(s) played a role in regulating steroidogenesis in Leydig cells.

Key words: Testis, Androgens, Leydig cells, Gonadal steroid hormones, Signal transduction