Total amounts of circulating human chorionic gonadotrophin α and β subunits can be assessed throughout human pregnancy using immunoradiometric assays calibrated with the unaltered and thermally dissociated heterodimer

The aim of the present study was to determine the variations in the balance between total (free plus combined) circulating α and β subunits of human chorionic gonadotrophin (hCG) throughout human pregnancy. The equivalence between the International Units (IU) of hCG (IRP 75/537) and those assigned to the α (IRP 75/569) and β (IRP 75/551) free subunits was experimentally determined by using intact and thermally dissociated hCG. Heat exposure (2 min at 100 o C) of hCG preparations resulted in a complete dissociation of hCG into free, soluble and intact α and β subunits. The hCG and α and β subunit contents of unaltered and heated hCG preparations were assessed by specific immunoradiometric assays