inhibin B

Inhibin B is the testis's status report to the brain about sperm production. When the seminiferous tubules are working well, the supporting cells send up this hormone as a signal saying, in effect, the factory is running, so ease off the stimulation.

Inhibin B is secreted mainly by the Sertoli cells, and its level reflects how healthy and active spermatogenesis is. Its job is to provide negative feedback specifically on follicle-stimulating hormone (FSH): when inhibin B is high, the pituitary releases less FSH. This is a more targeted feedback than testosterone provides, since testosterone suppresses both LH and FSH while inhibin B selectively restrains FSH.

Because it tracks Sertoli-cell activity, inhibin B is used as a marker of spermatogenesis and testicular function. A low inhibin B with a high FSH points to failure of the sperm-producing compartment, useful in evaluating male infertility or in children to assess whether functioning testicular tissue is present. It is not a perfect test, however, and is interpreted alongside semen analysis and other hormones rather than alone.