Placental production of human chorionic gonadotrophin α and β subunits in early pregnancy as evidenced in fluid from the exocoelomic cavity

Abstract

Levels of human chorionic gonadotrophin (hCG) and of its free alpha and beta subunits were measured using specific immunoradiometric assays in exocoelomic fluid (ECF) and maternal serum (MS) collected from five pregnant women at 6.6-8 weeks of gestation. Mean levels of hCG and its free subunits were significantly (P < 0.001) higher in ECF than in MS: 3.5-fold for hCG, 600-fold for free alpha hCG and 38-fold for beta hCG. There was no correlation between either hCG levels or levels of its free subunits in ECF and MS. On a molar basis, the quantity of free alpha hCG subunit expressed as a percentage of the total (free+combined) amount was 83% in ECF and 2.7% in MS (P < 0.001). The amount of free beta hCG subunit as a percentage of the total was 22% in ECF and 3.5% in MS (P < 0.001). The ratio of the total amounts of alpha- and beta hCG subunits amounted to 4.6 in ECF and 0.99 in MS (P < 0.001). The heterogeneity of hCG was further investigated by polyacrylamide gel electrophoresis followed by immunoblotting. Several bands with molecular mass ranging from 42 to 57 kDa, corresponding to hCG dimers, were immunodetected in ECF and MS with anti-alpha hCG and anti-beta hCG monoclonal antibodies. A free 35 kDa beta hCG immunoreactive band was found in ECF and MS. A free alpha hCG immunoreactive band was observed at 23 kDa in ECF and at 21 kDa in MS. These findings suggest that the exocoelomic cavity is a reservoir where hCG and its subunits produced by trophoblast accumulate directly.(ABSTRACT TRUNCATED AT 250 WORDS)