Which hormone stimulates Leydig cells in the testes to secrete testosterone?

• A. FSH
• B. Estrogen
• C. LH
• D. Adrenal androgens

Answer: (C)

Luteinizing hormone is the signal that directly tells Leydig cells to make testosterone. LH binds to receptors on these cells and activates a cascade (via cAMP) that increases the activity of the steroidogenic enzymes, converting cholesterol first to pregnenolone and then onward to testosterone. This is the primary mechanism for testosterone production in the testes, with GnRH from the hypothalamus regulating LH release in a pulsatile manner.

FSH, on the other hand, mainly targets Sertoli cells to support spermatogenesis, not testosterone secretion. Estrogen doesn’t trigger testosterone release from Leydig cells, though it’s involved in male physiology after being produced from testosterone. Adrenal androgens come from the adrenal glands, not from Leydig cells, and are not driven by LH in the testes.