Inhibin and activin subunits are differentially expressed in endometrial cells and leukocytes during the menstrual cycle, in early pregnancy and in women using progestin-only contraception

Inhibins and activins are dimeric hormones which share common subunits and which have diverse endocrine and paracrine roles in regulating reproductive function. Endometrial expression of inhibin alpha, ssA and ssB subunits was examined by immunohistochemistry and in-situ hybridization, across the menstrual cycle and in early pregnancy. All three subunits were found to be expressed in endometrium, primarily by glandular epithelium in the early stages of the cycle. Following the onset of decidualization, expression of alpha, ssA and ssB subunits was up-regulated in decidualized stromal cells. A marked down-regulation of alpha subunit was detected in glandular epithelium, whilst expression of ssA and ssB subunits was maintained. This pattern was consistent in decidua from early pregnancy and additionally in endometrium from women using progestin-only contraceptives, either subdermal implants (Norplant((R))) or levonorgestrel-releasing intrauterine systems (Lng-IUS). Immunostaining was also observed for both ssA and ssB subunits in subpopulations of endometrial leukocytes, identified to be distinct subsets of macrophages, neutrophils and mast cells. Potential paracrine roles for activins may be envisaged in facilitating tissue remodelling during decidualization, in tissue repair following menstruation, and additionally in modulating premenstrual inflammatory events.