Index
It is a hormone secreted in response to follicle-stimulating hormone (FSH).
In turn, this hormone eventually suppresses the production and release of FSH from the pituitary gland.
Inhibin plays an important role in male and female reproductive development. The reproductive organs are the main source of inhibin, although it can also be found in the prostate, brain, and adrenal glands.
Activin is another sex hormone that increases the production of FSH and gonadotropin-releasing hormone (GnRH). Inhibins suppress this increase in FSH and GnRH by blocking the binding of activin to its receptors.
There are two forms of inhibin: inhibin A and B.
Inhibina A y B
Inhibins are protein complexes with two units linked to each other. These are called inhibin A and B.
Blood inhibin A and B levels vary throughout the menstrual cycle. Inhibin A levels are highest during the later follicular and luteal phases of a normal menstrual cycle, while inhibin B dominates in the early and middle follicular phases and decreases in the late follicular phase.
During the late luteal phase, inhibin A levels decline, allowing FSH levels to rise. This activity plays a role in biological changes within a menstrual cycle.
In contrast, males only produce inhibin B, which is produced in the testes by Sertoli cells. Inhibin B production and secretion change during testis development, and FSH secretion is increased or decreased by inhibin B depending on the sperm production process.
Inhibin production
FSH stimulates the production of inhibin by the granulosa cells of the ovaries and the Sertoli cells of the testes.
Other factors that increase inhibin production include:
- IL-1beta (para inhibin A).
- IGF-1 (para inhibina A).
Factors that reduce inhibin production include:
- Progesterone.
- IL-1 (para inhibin B).
In women, inhibin secretion increases as the follicle matures. This improves the activity of aromatase, the enzyme involved in the production of estrogen.
The roles of inhibin
Inhibin maintains male reproductive function
Inhibin B, which is produced in the testes by Sertoli cells, is the active form of inhibin in men. As inhibin B levels in the blood increase, FSH levels decrease.
Higher blood levels of inhibin B increase the number of Sertoli cells and sperm production in healthy fertile men.
Inhibin increases sperm production
Inhibin B is a marker for sperm production and male reproductive health. Inhibin blood levels were reduced in 104 men with various testicular disorders compared to normal men.
In a study of nearly 1,800 fertile men, elevated blood levels of inhibin B were associated with increased sperm count and concentration.
Normal ebb and flow of inhibin is important for fertility
In women, inhibins A and B have a different pattern of secretion throughout the menstrual cycle. Decreased inhibin B secretion decreases the ovarian follicular group in women and leads to infertility.
Also, inhibin levels during pregnancy are higher than those during a normal menstrual cycle.
Because inhibins are produced by the placenta and fetal membranes, they can be used to diagnose fertility problems and early pregnancy.
A mutation in the inhibin gene is associated with premature ovarian failure (POF). This causes a reduction in inhibin B activity and therefore inhibin B levels are used to detect POF and ovarian recovery in women with problems associated with the hypothalamus.
Additionally, both inhibin A and B can be used to assess ovarian function in patients with Turner syndrome, a genetic disorder.
Total inhibin levels in the blood are also used in the diagnosis of patients with polycystic ovary syndrome (PCOS) and ovarian tumors.
Inhibin increases ovarian health
The ovarian reserve is the ability of the ovaries to produce eggs capable of fertilization for a successful pregnancy. Decreased levels of inhibin B were observed in women with decreasing ovarian reserve.
Women with low levels of inhibin B in the blood also showed a reduced response to ovulation stimulation and a lower chance of getting pregnant, naturally or with assisted reproduction.
Inhibins improve the health and development of ovarian follicles. Higher levels of inhibin A and B in follicular fluid also increase pregnancy rates.
Inhibin may be involved in eye development
In the developing mouse eye, inhibin was observed in the lens and cells between the lens and the optic disc. It was also found in various cell layers of the retina. These results suggest that inhibin may be involved in retinal development.
Similarly, in the adult rat eye, an inhibin subunit (α subunit) was detected in light-responsive cells of the retina.
Inhibin can reduce blood cell production
Inhibins reduce human blood cell production by suppressing the activity of human bone marrow cells.
Decreased production of bone marrow and spleen cells was observed after injection of inhibin (into the vein) in mice.
Conditions associated with low levels of inhibin
Inhibin in ectopic pregnancy
An ectopic pregnancy occurs when the fertilized egg attaches to other sites besides the uterus. Reduced levels of inhibin in maternal blood were observed in ectopic pregnancies compared to normal pregnancies.
Similarly, another study found lower blood inhibin A levels in patients with ectopic pregnancies and abnormal pregnancies involving miscarriages. These results indicate that inhibin levels can be used as a marker for abnormal or ectopic pregnancies.
Inhibin plays a role in menopause
During menopause, the ovarian follicles, the levels of inhibin, estrogens and androgens are reduced, while the levels of FSH increase. As a result of these changes, the menstrual cycle becomes irregular.
In women over the age of 40 with periods, high FSH levels were only associated with reduced levels of inhibin B in the blood but not with levels of inhibin A.
The luteal phase is also affected by age. In older women, during this phase, progesterone levels remain stable but inhibin A levels drop.
Premature ovarian failure (PFO) and inhibition
FOP is a condition associated with loss of menstruation, infertility, and increased levels of sex hormones in women under 40 years of age. In these women, the levels of inhibin A and B in the blood are lower, while the FSH is higher.
Inhibin reduces bone activity
The bone activity of bone removal and replacement takes place throughout the body. Bone mass is maintained through a balance of bone formation and bone loss. Inhibin inhibited both activities in the bone marrow of mice.
Studies in menopausal women showed that increasing levels of inhibin B reduced bone density.
Low levels of inhibin in the blood were associated with increased markers of bone formation and bone loss in pre and perimenopausal women.
However, in mice, high levels of inhibin A increased bone mass and strength.
Inhibin and male infertility
Inhibin B is important for Sertoli cell development and sperm production.
Low levels of inhibin B reduce sperm production and can lead to testicular problems. Therefore, inhibin B is useful in predicting male infertility.
In a clinical study of 160 men, blood levels of inhibin B were used as a marker of male infertility.
Conditions associated with high levels of inhibin
Elevated Inhibin May Indicate Ovarian Cancer
Ovarian cancer is one of the most common cancers in women, and inhibins play a role in its development.
Inhibin B is the main form of inhibin secreted by granulosa cell tumors. Total inhibin levels were elevated in six postmenopausal women with granulosa cell tumors.
Blood levels of inhibins were also increased in women with mucin-producing epithelial cell cancers.
Elevated Inhibin May Predict Pregnancy Loss
Inhibin A levels in the blood increase throughout pregnancy. They remain low during the first and second trimesters and then rise during the third trimester.
In the later stages of pregnancy, the fetal placenta becomes the main source of inhibin. In a miscarriage study, a significant decrease in maternal blood inhibin A levels was observed.
Therefore, inhibin A may be helpful in predicting miscarriage and early pregnancy loss.
Inhibin A can also predict fetal survival during early pregnancy in women undergoing in vitro fertilization (IVF). Increased pregnancy loss was observed in women with lower blood inhibin A after IVF.
Inhibin acts as a tumor marker
Inhibin is secreted by all granulosa cell tumors of the ovary and can be used as a tumor marker to determine response to treatment. Inhibin in the blood is also significantly increased in breast cancer.
However, women with breast cancer who underwent surgery showed decreased levels of inhibin in their blood, indicating that these tumors may be secreting inhibins.
Inhibins can also be used as a marker to diagnose breast cancer in postmenopausal women. In these women, inhibin levels were already very low, therefore any change in inhibin levels was helpful in detecting a tumor.
High inhibin may indicate Down syndrome
The risk of having a child with Down syndrome is highest among women over 35 years of age. The link between increased inhibin in the blood and Down syndrome was seen in several studies.
Inhibin A is used in the test done to predict the risk of Down syndrome.
Elevated inhibin is associated with preeclampsia
Preeclampsia is a pregnancy complication that causes high blood pressure and organ damage after 20 weeks of pregnancy. Inhibin is a marker for the detection of preeclampsia.
Blood inhibin A levels were increased in women with pre-eclampsia compared to those with a normal pregnancy. Elevated maternal inhibin A levels are also associated with greater severity of pre-eclampsia.
Normal blood levels of inhibin
In men
- Inhibin A levels: <2 pg / ml.
- Inhibin B levels: Infertile men 78 pg / ml; Fertile men 138 pg / mL.
In women
- Inhibin A levels: premenopausal women 2-80 pg / ml; Postmenopausal women are <5 pg / ml.
- Inhibin B levels: premenopausal women <200 pg / ml; Postmenopausal women are <15 pg / ml.
In pregnant women
- Inhibina A: 1.8–2.31 ng / ml (week 8); 2 ng / ml (weeks 8-24); 24-30 ng / mL por (week 38).
- Inhibina B: <12 pg / ml (semana 5-16); 19-31 pg / ml (semana 36).
You can have too little of this hormone if:
For women:
- You are in menopause.
- You have hot flashes.
- You have irregular or absent menstrual periods.
- You are infertile or have trouble getting pregnant.
Because inhibin levels vary throughout the menstrual cycle, inhibin levels in premenopausal women must be interpreted carefully.
For men:
- You have a low sperm count.
- You are infertile.
- He has smaller testicles.
It is important to note that these symptoms or conditions do not necessarily indicate lower or higher levels of inhibin in the blood. A blood test should be used to determine these levels and the results should always be discussed with a doctor.
You can have too much of this hormone if:
For women:
- You have complications during pregnancy, such as pre-eclampsia.
- You have polycystic ovary syndrome.
- You have ovarian cancer.
For men:
Little is known about how higher inhibin levels affect men.
Ways to lower inhibin
Biological substances that decrease inhibition
- Progesterone.
- IL-1 (para inhibin B).
Treatments that lower inhibin
- Hypophysectomy: Surgical removal of the pituitary gland in rats caused a decrease in inhibin levels in the blood.
Ways to increase inhibin
Biological substances that increase inhibition
- IL-1beta (para inhibin A).
- IGF-1 (para inhibina A).
Treatments that increase inhibin
- Varicocele treatment : Varicocele treatment (varicose veins in the scrotum) increased blood levels of inhibin b in infertile men.
- Human Chorionic Gonadotropin (hCG) Treatment : HCG treatment in healthy men significantly increased blood levels of inhibin.
Lifestyle factors that increase inhibition
- Losing weight: Inhibin B levels decrease with increasing weight in men and women.
- Smoking cessation: smoking history was negatively correlated with inhibin b levels in older women of reproductive age.
