Inhibin is an important hormone for male and female reproductive health. It is involved in the development of reproductive organs, fertility, and pregnancy. It also serves as a diagnostic marker for a variety of body functions and conditions. Read on to learn more about the roles of inhibin, normal blood levels, and conditions associated with high and low levels of this hormone.<\/p>\n
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Inhibin is a hormone secreted in response to FSH<\/a> [R<\/a>].<\/p>\n In turn, inhibin ultimately suppresses the production and release of FSH from the pituitary gland [R<\/a>].<\/p>\n Inhibin plays an important role in male and female reproductive development [R<\/a>, R<\/a>, R<\/a>].<\/p>\n Reproductive organs are the main source of inhibin, although it can also be found in the prostate, brain, and adrenal glands [R<\/a>].<\/p>\n Activin is another sex hormone that increases FSH and gonadotropin-releasing hormone<\/a> (GnRH) production. Inhibins suppress this increase in FSH and GnRH by blocking the binding of activin to its receptors [R<\/a>].<\/p>\n There are two forms of inhibin, inhibin A and B [R<\/a>].<\/p>\n Inhibins are protein complexes with two units linked to each other. These are called inhibin A and B [R<\/a>].<\/p>\n Blood inhibin A and B levels vary throughout the menstrual cycle. Inhibin A levels are highest during the late follicular and luteal phases of a normal menstrual cycle, whereas inhibin B dominates in the early and mid follicular phases and declines in the late follicular phase [R<\/a>, R<\/a>].<\/p>\n During the late luteal phase, inhibin A levels drop, allowing FSH levels to increase. This activity plays a role in the biological changes within a menstrual cycle [R<\/a>, R<\/a>].<\/p>\n In contrast, males only produce inhibin B<\/strong>, which is produced in the testis by the Sertoli cells. Inhibin B production and secretion changes during the development of testis, and inhibin B increases or decreases the secretion of FSH depending on the sperm production process [R<\/a>].<\/p>\n FSH stimulates the production of inhibin<\/strong> by the granulosa cells of the ovaries and the Sertoli cells of the testes [R<\/a>].<\/p>\n Other factors that increase inhibin production include:<\/p>\n Factors that reduce inhibin production include:<\/p>\n In females, inhibin secretion increases as the follicle matures. This enhances the activity of aromatase, the enzyme involved in the production of estrogen<\/a> [R<\/a>].<\/p>\n Inhibin B, which is produced in the testis by the Sertoli cells, is the active form of inhibin in men.<\/strong> As blood inhibin B levels increase, FSH levels decrease. Higher blood levels of inhibin B increase the number of Sertoli cells and sperm production in healthy fertile males [R<\/a>, R<\/a>].<\/p>\n Inhibin B is a marker of sperm production and male reproductive health. Blood inhibin levels were reduced in 104 men with various testicular disorders as compared to normal men [R<\/a>, R<\/a>].<\/p>\n In a study with nearly 1,800 fertile men, elevated blood inhibin B levels were associated with increased sperm count and concentration [R<\/a>].<\/p>\n In women, inhibins A and B have a different pattern of secretion throughout the menstrual cycle [R<\/a>].<\/p>\n Decreased inhibin B secretion decreases the ovarian follicular pool in women and leads to infertility [R<\/a>].<\/p>\n Also, inhibin levels during pregnancy are higher than those during a normal menstrual cycle [R<\/a>].<\/p>\n Because inhibins are produced by the placenta and fetal membranes, they may be used to diagnose fertility problems and early pregnancy [R<\/a>].<\/p>\n A mutation in inhibin gene is associated with premature ovarian failure (POF). This causes a reduction in inhibin B activity, and thus, inhibin B levels are used to detect POF and ovarian recovery in women with hypothalamus<\/a>-associated problems [R<\/a>, R<\/a>].<\/p>\n Additionally, both inhibin A and B can be used to assess the function of the ovaries in patients with Turner syndrome, a genetic disorder [R<\/a>].<\/p>\n Total inhibin levels in the blood are also used in the diagnosis of patients with polycystic ovary syndrome (PCOS) and ovarian tumors [R<\/a>].<\/p>\nInhibin A and B<\/strong><\/span><\/h3>\n
Production<\/strong><\/span><\/h3>\n
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Roles of Inhibin<\/span><\/h2>\n
1) Maintains Male Reproductive Function<\/strong><\/span><\/h3>\n
Sperm Production<\/h4>\n
2) Supports Female Reproductive Function<\/strong><\/span><\/h3>\n