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What Is the Role of Inhibin?

S. Berger
S. Berger

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 A levels may predict Down's syndrome.
Inhibin A levels may predict Down's syndrome.

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.

Inhibin plays an important role in a woman's fertility.
Inhibin plays an important role in a woman's fertility.

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.

Inhibin plays a role in the female reproductive system.
Inhibin plays a role in the female reproductive system.

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.

Discussion Comments

SteamLouis

@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.

ysmina

@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.

burcinc

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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    • Inhibin A levels may predict Down's syndrome.
      By: karelnoppe
      Inhibin A levels may predict Down's syndrome.
    • Inhibin plays an important role in a woman's fertility.
      By: John Takai
      Inhibin plays an important role in a woman's fertility.
    • Inhibin plays a role in the female reproductive system.
      By: blueringmedia
      Inhibin plays a role in the female reproductive system.
    • Inhibin plays a role in the aging process.
      By: Gianfranco Bella
      Inhibin plays a role in the aging process.
    • Higher levels of inhibin B in males has been associated with fertility.
      By: WavebreakMediaMicro
      Higher levels of inhibin B in males has been associated with fertility.
    • During ovulation, and the mid-follicular phase, inhibin B is produced, and during the mid-luteal phase, more inhibin A is secreted.
      By: joshya
      During ovulation, and the mid-follicular phase, inhibin B is produced, and during the mid-luteal phase, more inhibin A is secreted.
    • Changes in the production of inhibin and activin may result in bone turnover, even before the onset of menopause.
      By: Lisa F. Young
      Changes in the production of inhibin and activin may result in bone turnover, even before the onset of menopause.