Inhibin is a peptide hormone that inhibits FSH (Follicle Stimulating Hormone) synthesis and secretion, and contributes to regulation of the menstrual cycle (Wikipedia, 2007).
It is made up of alpha and beta subunits that are linked by disulfide bonds. The alpha subunits remain identical while the beta subunits differ (A or B), creating two forms (McCullagh, R., 2003). Therefore, inhibin belongs to the transforming growth factor - B (TGF-B) family (J Clin, 2005).
In females, FSH stimulates the secretion of inhibin (A and B) from the granulosa cells of the ovary, and inhibin in turn, suppresses FSH (Kipp et al., 2007). These peptides are diminished by GnRH and enhanced by insulin like growth factor - 1 (IGF-1) (Wikipedia, 2007). Both forms (A and B) peak at different times during the menstrual cycle. Inhibin B peaks between early and mid follicular phase and then peaks for the second time during ovulation. Inhibin A peaks during mid-luteal phase (Wikipedia, 2007).
In men, inhibin is found only in its B form. It inhibits FSH production as in the females, and is produced by the testes (McCullagh, R., 2003).
These peptides are also commonly used for prenatal testing. The prenatal quad screen is typically administered at a gestational age of 16-18 weeks. If results show elevated inhibin A ( with increased beta-hCG, and decreased AFP and estriol) a fetus with down syndrome is assumed ( New England Journal of Medicine, 2006).
References:
Inhibin. (2006, December 7). In Wikipedia, The Free Encyclopedia. Retrieved 15:47, January 30, 2007, from http://en.wikipedia.org/w/index.php?title=Inhibin&oldid=92601534
J Clin Endocrinol Metab. 2005 Jan; 90(1); 271-8. Epub 2004 Oct 13.
Kipp et al., Endocrinology, 2007 Jan 25, [Epub ahead of print] "Neonatal Exposure to Estrogens Suppresses Activin Expression and Signaling in the Mouse Ovary."
"Dimerk Inhibin A as a marker for Down's Syndrome in Early Pregnancy". New England Journal of Medicine, The 334(19); 1231-1236. Retrieved 2006-08-04.
McCullagh, R. (2003). Inhibin. Inhibin Fertility and Reproduction Function. Retrieved January 29th 2007 from http://www.inhibin.com/Home/Static.aspx?PageID=0
