Sunday, 26 July 2020

Inhibin-B a marker of Ovarian reserve


What, as Gynaecologist we need to know on Inhibin-B?
Inhibin is a dimeric glycoprotein complex that suppresses the secretion of FSH by the pituitary gland. Inhibins are hormones secreted by granulosa cells of the ovary in the female and Sertoli cells of the testis in the male. They selectively suppress the secretion of pituitary follicle stimulating hormone (FSH) and also have local paracrine actions in the gonads. The inhibins consist of a dimer of 2 homologous subunits, an alpha subunit and either a beta A or beta B subunit, to form inhibin A and inhibin B, respectively. Inhibin-b are produced by the 1) gonads by Sertoli cells in particular in men and 2) by granulosa cells in women. Inhibin plays a vital role in controlling the production of gametes and embryonic and the foetal development. They selectively suppress the secretion of pituitary follicle stimulating hormone (FSH) and also have local paracrine actions in the gonads.
Reference Values
Males: <2.0 pg/mL
Females
<11 years: <4.7 pg/mL
11-17 years: <97.5 pg/mL
Premenopausal: <97.5 pg/mL
Postmenopausal: <2.1 pg/mL


The inhibins consist of a dimer of 2 homologous subunits, an alpha subunit and either a beta A or beta B subunit, to form inhibin A and inhibin B, respectively. 
In females, inhibin A is primarily produced by the dominant follicle and corpus luteum: whereas inhibin B is predominantly produced by small developing follicles. Serum inhibin A and B levels fluctuate during the menstrual cycle. At menopause, with the depletion of ovarian follicles, serum inhibin A and B decrease to very low or undetectable levels. Inhibins are glycoproteins produced by the granulosa and theca cells of the ovary and belong to the superfamily of transforming growth factors-β (TGFs-β).  Role of inhibin includes suppression of FSH production from the pituitary.  Levels of inhibit B vary with exogeneous GnRH or FSH stimulation and also between menstrual cycles. Levels are lower (<45 pg/ml) in women who are poor responders. Women with reduced ovarian reserve have reduced values of estradiol (E2) up to 50 pg/ml.  When measured along with basal FSH, increased day 3 estradiol reflects a poor response to ovarian stimulation. Early elevation of estradiol reflects the advanced follicular development and early selection of dominant follicle.

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