LOCALIZATION OF THE CELLULAR EXPRESSION OF INHIBIN IN TROPHOBLASTIC TISSUE

Aims: Inhibin is a peptide hormone which is normally produced by ovari an granulosa cells and which inhibits the release of follicle stimulat ing hormone from the pituitary gland, thus acting as a modulator of fo lliculogenesis. Serum inhibin levels are higher during pregnancy than during the normal menstrual cycle and the placenta is thought to be a source of circulating inhibin. Previous studies hare yielded conflicti ng results as to the cellular localization of inhibin in the placenta and the aim of the present study was to investigate the immunohistoche mical localization of the hormone in placental tissue. We also wished to investigate whether inhibin could be demonstrated in choriocarcinom a and in non-gestational trophoblastic tissue. Materials and results: Immunohistochemical staining was performed using a monoclonal antibody against the of subunit of human inhibin, Specimens included in the st udy were intrauterine products of conception (n=36), extrauterine prod ucts of conception (n=4), decidualized endometrium (n = 15), extrauter ine decidualized tissue (n = 3), hydatidiform mole (n = 5), uterine ch oriocarinoma (n = 2) and testicular embryonal carcinoma with syncytiot rophoblast giant cells (n = 6). In cases of products of conception, in cluding hydatidiform mole, there was consistent strong positive staini ng of syncytiotrophoblast but no staining of cytotrophoblast with anti -inhibin. Staining with anti-inhibin highlighted trophoblastic cells w ithin the placental bed, in a small number of cases there was focal we ak positive staining of decidua. There was positive staining of the tw o cases of uterine choriocarcinoma and of syncytiotrophoblast giant ce lls in the six cases of testicular embryonal carcinoma. Conclusions: T he study shows that immunohistochemically detectable inhibin alpha sub unit in placental tissue is mainly localized within syncytiotrophoblas t although in some cases there is also positive staining of decidua. P roduction of inhibin by these cells may account for raised serum level s during pregnancy Inhibin can also be demonstrated in choriocarcinoma and in non-gestational trophoblastic tissue, Inhibin is a sensitive m arker of syncytiotrophoblast and staining with this antibody may prove useful in the diagnosis of choriocarcinoma and in the demonstration o f trophoblastic cells in germ cell tumours.