What Is the Role of Inhibin?

Inhibin is a hormone that occurs in both men and women. Playing an integral role in the reproductive system, it may also have a non-reproductive involvement in the aging process. In women, the hormone is secreted in the ovaries, and acts to prevent the synthesis and secretion of follicle-stimulating hormone (FSH). FSH actually stimulates the secretion of inhibin, so the latter hormone is part of a feedback mechanism to prevent an overabundance of FSH. This feedback cycle, in turn, has a cascade effect that contributes to the cyclical nature of female fertility.

Both males and females produce FSH and gonadotropin-releasing hormone (GnRH), and inhibin prevents this release in both genders. In women, the hormone produced in the gonads, placenta, and pituitary gland accomplishes this goal. In males, testicular Sertoli cells secrete the needed inhibin. Males also use this in the testes as a means of regulating sperm production. The presence of androgen increases inhibin levels, which in turn seems to promote spermatogenesis.

Inhibin performs the opposite role of the hormone activin in the menstrual cycle. Activin promotes FSH secretion, which in turn helps to ensure the development of ovarian follicles. This hormone may compete with activin for similar receptors, or bind to its own receptor, to serve as a counterweight to activin. During different phases of ovulation, one of two forms may be active. During ovulation, and the mid-follicular phase, inhibin B is produced, and during the mid-luteal phase, more inhibin A is secreted.

The opposite effects of activin and inhibin are shown in their effects on bone development in aging. While activin promotes bone growth and differentiation, inhibin suppresses these effects, even in the presence of activin. Changes in the production of both hormones may result in bone turnover, even before the onset of menopause. The decline in inhibin in both genders over time could increase the risk of certain bone-related conditions.

While its exact role in pregnancy is not yet known, it also has a role as an indicator for both pregnancy and male fertility. Inhibin A levels could serve as a predictor of Down's syndrome in the fetus, fetal growth restriction, and miscarriage, even before clinical symptoms appear. In males, higher levels of inhibin B has been significantly associated with fertility. Tests for these conditions have been recommended as predictors because it has a shorter half life than the hormones normally measured to detect them.

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Post 3

@ysmina-- An inhibin test is also being used to diagnose ovarian cancer now, isn't it?

I have ovarian cancer in my family history and I remember reading an article about this recently. I don't think checking for inhibin helps diagnose all kinds of ovarian cancer however. I believe it only helps diagnose ovarian cancers that have to do with the egg cells.

I also don't know if this is used as a screening test or a supporting test for the diagnosis. I believe it's fairly new, so maybe the verdict is still out for it.

Inhibin is clearly a really important hormone in the reproductive system though. I'm glad that medical researchers are learning more about its functions and using that towards new diagnosis methods.

Post 2

@burcinc-- You are absolutely right. The inhibin B test can tell you what your egg reserve is like, as well as how healthy they are.

But it's not because inhibin B is necessary for ovulation. It's the ovaries that actually produce inhibin B hormone. So what the test will do is check for the amounts of inhibin B in your blood. The higher inhibin B levels are in your blood, the more eggs you have in your reserve. So that's why an inhibin B test is used.

Post 1

My husband and I have been trying to conceive for the past six months without any success. My doctor has told me that I will need to get an "inhibin B test" to check my egg numbers.

She was in a rush when she told me this so I couldn't ask for more details. I'm scheduled to have the test in two weeks.

What does inhibin B have to do with the number of eggs? I know the article said that inhibin B is produced during certain phases of ovulation. Will this test tell me how many eggs I have and how healthy they are?

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