Inhibin B

Where it comes from

Made in

Granulosa cells of small growing follicles; Sertoli cells of the testis

Sent out by

Early in the follicular phase in women; steady in men, in proportion to sperm production

Acts on

• Pituitary gonadotrophs (FSH)

What it does

• Reports the pool of growing follicles to the pituitary
• In men, the Sertoli cell’s feedback on FSH, and the closest blood measure of sperm production ¹
• Falls before FSH rises in the approach to menopause ³

In medicine

• Measured in men with infertility, where it tracks spermatogenesis and is absent in Sertoli cell-only testes ¹
• An older marker of ovarian reserve, largely replaced by anti-Müllerian hormone, which varies less across the cycle
• Measured in boys with testes that cannot be felt: with anti-Müllerian hormone it tells working testicular tissue from none, and can spare a laparoscopy ²

Beyond the body’s own use

• Not a medicine and not a target. The whole interest is as a test, and the argument is over which marker to use rather than whether to give it
• Because it falls before FSH rises, it was studied as an early marker of the menopausal transition ³; it never became a test of when menopause will come, and anti-Müllerian hormone is used instead