Inhibin: an Overlooked Ovarian Hormone

Hardly a medical visit goes by to the gyno office without discussing estrogen or progesterone, and often we get blood tests for it as well. But the granulosa cells of the ovary that make estrogen, make many more substances as well, so your gyno says there is another ovarian hormone. Actually there are several other ovarian hormones besides just the estrogen and progesterone.. Inhibin, activin and follistatin are all made at the same time as estrogen, and in response to the same hormone, FSH (follicle stimulating hormone), that stimulates estrogen production and the formation of a healthy egg. Actually, just as estrogen has many activities on many cells and in many organs, these molecules do as well. We do run tests of inhibin when performing birth defect screening in pregnancy, it's one of the four tests in the "Quad Screen". that is done for birth defect screening at 18 weeks of pregnancy. Inhibin has a very unique roll in our fertility: it's responsible for the signals that cause one egg to be ripe and be fertilized, and the other eggs that have started to mature will die at the instructions from inhibin! There are two forms of the molecule, inhibin-A and inhibin-B. The chemical signal that shifts inhibin from one to the other is controlled by the brain secretion of GnRH which is what also controls LH (luteinizing hormone) and FSH. And abnormalities of inhibin-B can cause your periods to be off even if your levels of estrogen and progesterone test normal. So next time you have a gyno hormone mystery to solve, think about some of the more silent factors in the ovaries such as these lesser known hormones, and it may help you understand your cycles better.

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