Characterization of the human chorionic gonadotrophin fractions in pregnancy urine

The human chorionic gonadotrophin (hCG) preparation (ca. 3000 IU/mg) from pooled pregnancy urine has been fractionated using anion-exchange and gel exclusion chromatography. The various fractions, many of which were heterogeneous, were assayed using radioimmunoassay (RIA) and a testicular radio-receptor assay (RRA). Three fractions were obtained with potencies between 9000 and 20 000 IU/mg); five fractions were characterized by potencies between 1000 and 6000 IU/mg; and four fractions exhibited low potencies (less than 500 IU/mg). A linear relationship between RRA and RIA potency (P) was found to exist for the various fractions: In(PRRA) = 1.14 In(PRIA) - 1.67. The major fractions, which exhibited various potencies, were further characterized by amino acid and carbohydrate analysis. Urine was collected from an individual at various times of gestation, and the hCG fraction was concentrated by benzoic acid and ethanol precipitation. Ion-exchange chromatography of the hCG fraction yielded multiple immunoreactive components throughout pregnancy; thus the observed heterogeneity in the commercial preparation does not appear to result from processing pooled urine from numerous donors. Also, heterogeneity was observed in an individual donor whose urine was not treated with the benzoic acid and alcohol fractionation scheme. It seems indisputable that individual urinary hCG is heterogenous, and this does not appear to reflect isolation artefacts.