Inhibins and Activins as Possible Marker of Ectopic Pregnancy

The regulation of reproduction is performed by complex hormonal system: hypothalamus pituitary ovary. There are a lot of ovarian peptides, playing an essential role in the regulation of this hormonal system. However, the mechanisms of their action are not exactly elucidated. Within ovarian peptides, inhibins are seemed to be consider as very important. The term “inhibin” was indicated by McCullagh in 1932. He described inhibin as a hydrophilic substance and an extract from male gonads, which inhibits the pituitary gland. However, only 53 years later, the isolation of inhibin from follicular fluid in cows for the first has been performed. Inhibin was characterized as a glycoprotein, consisting of two subunits linked by disulfide bond (Yamaguchi et al, 1991). Inhibins belong to the superfamily of transforming growth factor ┚ (TGF-┚). This family contains about 30 peptides, including activin, Anti-Müllerian Hormone (AMH), epithelial growth factor (epidermal growth factor EGF) and the subfamily of transforming growth factor-┚ (TGF-┚) (de Kretser et al., 2002).Inhibins (inhibin A, B, total inhibin) play a very important role in the regulation of female reproduction. Inhibins are glycoprotein substances produced mainly in the ovaries and they take part in the regulation of menstrual cycle. They consist of a glycosylated subunit ┙ combined with disulfide bond with one of two different subunits β (betaA or betaB). The resulting inhibin are properly labeled as inhibin A (alpha betaA) and inhibin B (alpha betaB) (Burger & Igarashi, 1988). Inhibins play an important role in reproductive functions by regulating pituitary folliclestimulating hormone (FSH) secretion during the menstrual cycle. This regulation is processed by a feedback mechanism. FSH stimulates the maturation of ovarian follicles, where granulosa cells produce inhibins. Increased levels of inhibins in the peripheral blood subsequently inhibit the secretion of FSH (Muttukrishna et al., 2000). There are studies about possible use of inhibins in reproductive medicine. Inhibin A is secreted mainly by the dominant follicles and corpus luteum of the ovary. In addition, the sources of this peptide are also adrenal, pituitary, spleen, bone marrow, placenta and fetal membranes (Petraglia et al., 1999). Recent data indicates the evaluation of inhibin A concentration mainly in the obstetric diagnosis (Florio et al., 2004).