What is the inhibin
Inhibin is a glycoprotein hormone belonging to the superfamily of transforming ß growth factors (TGF-ß), which also includes activin. Two forms are known: inhibin A and inhibin B, both consisting of two alpha and beta subunits (respectively α - Β A and α - Β B ).
Functions
The main biological role of inhibin consists in selectively suppressing the secretion of the pituitary follicle stimulating hormone or FSH. This hormone, also known as FSH, promotes spermatogenesis in humans, or the synthesis of new spermatozoa, while in women it induces maturation of ovarian follicles.
Inhibin is mainly secreted by the granulosa cells of the ovary in women and by testicular cells of Sertoli in humans. Its inhibitory action on the secretion of FSH occurs through the inhibition of the activin, which instead carries out a stimulating activity.
Inhibin decreases the biosynthesis and release of FSH, while the activin increases them.
Clinical meaning
The dosage of inhibin A is part of the so-called quadruple-test, a screening test carried out around the 16th-18th week of pregnancy to identify pregnant women with the highest risk of carrying fetuses with Down syndrome in the womb. This risk is considered high when the mother has high blood levels of inhibin A and human chorionic gonadotropin, associated with a reduction in those of estriol and alpha-fetoprotein. Being a screening test, high-risk pregnant women are directed towards more specific tests and diagnostic tests, such as amniocentesis.
The inhibin B dosage in humans can be used as a marker of spermatogenesis and male fertility . In particular, very low levels of inhibin B indicate insufficient or zero sperm production and advise against proceeding to take them from the testicle using the TESE method. More generally, the average levels of inhibin B in fertile men are higher than those of individuals with infertility problems.
Also in the area of assisted fertilization, inhibin B can be used, in the same way as estradiol, to control follicular growth (control of superovulation cycles). The inhibin B dosage also allows an evaluation of ovarian reserve and prediction of ovulation induction.
The dosage of inhibin blood levels has also been proposed as tumor markers of ovarian cancer, in particular of the forms that affect the granulosa cells.
