Distribution of the beta-core human chorionic gonadotrophin fragment in human body fluids

The origins of a fragment of the human chorionic gonadotrophin (hCG) molecule, beta-core (beta C-hCG) were studied by analysis of beta C-hCG concentrations in biological fluids. In addition, the ability of the placenta to produce the fragment and the metabolism of hCG to beta C-hCG by human granulosa cells was determined in tissue culture. Finally the conversion of exogenous hCG to beta C-hCG was studied in vivo. The fragment was present in pregnancy urine as well as that from premenopausal and postmenopausal subjects. The highest concentrations were found in pregnant women. Ratios of beta C-hCG to intact hCG were higher in pregnancy urine when radioimmunoassay (RIA) was used compared with immunoradiometric assay (IRMA) (0.67 and 0.37 respectively). Concentrations of beta C-hCG were higher in postmenopausal urine than in premenopausal specimens. A significant amount of a high molecular weight beta C-hCG immunoreactive material was found in serum samples after size separation, and the molar ratio of beta C-hCG/hCG was estimated as 0.019. Amniotic fluid also contained small quantities of two forms of immunoreactive beta C-hCG and the ratio of 0.01 for authentic beta C-hCG/hCG increased to 0.026 when the high molecular weight form was considered. Cultured trophoblastic tissue released material with beta C-hCG immunoreactivity in the medium and chromatographic separation revealed that the majority of this material was of higher molecular weight compared with the authentic beta C-hCG form. beta C-hCG was the principal glycoprotein found in follicular fluid after hyperstimulated folliculogenesis and intramuscular injection of 5000 IU hCG. We also demonstrated that 26% of follicular fluid samples (n = 50) were positive for beta C-hCG; levels ranged from 5.2 to 23.0 pmol/l (13.1 +/- 5.7); S.D.) when a specific IRMA was used. The RIA could detect beta C-hCG in 48 samples (96%), levels ranging from 7.0 to 28.5 pmol/l (19.4 +/- 5.2). Moreover, granulosa cells cultured in the presence of hCG were able to degrade the intact molecule to both high molecular weight and authentic immunoreactive forms of beta C-hCG. After gel filtration, material of molecular weight over a wide range and immunoreactive for beta C-hCG was present in human seminal plasma. Assaying 74 samples of this fluid by IRMA, beta C-hCG was detected in 42 (56.7%), levels ranging between 5.5 and 59.5 pmol/l (24.9 +/- 15.2).(ABSTRACT TRUNCATED AT 400 WORDS)