Concentrations of 2-methoxyoestrogens in human serum measured by a heterologous immunoassay with an 125I-labelled ligand.

A radioimmunoassay has been developed for the measurement of 2-methoxyoestrogens in samples of human serum without chromatography after solvent extraction. Antibodies raised against 2-methoxyoestradiol-17 beta-hemi-succinyl-BSA served as binding protein and 2-methoxyoestrone-17-cmo-[125I]iodohistamine served as 125I-labelled ligand. A specific (little or no cross-reactivities to other oestrogens), sensitive (2.4 +/- 0.9 pg/tube) and precise (6.5% intra-assay; 9.1% inter-assay) assay was obtained by employing the heterologous bridge system. The following concentrations were found in serum samples of healthy subjects (median, range in parentheses): men (19-58 years): less than 10.3 (less than 10.3-35.5) pg/ml (n = 22); women follicular phase: 46 (18-63) pg/ml (n = 8); luteal phase: 70 (31-138) pg/ml (n = 8); post-menopausal women: 33 (21-76) pg/ml (n = 10); pregnant women 11th-16th week: 674 (216-1678) pg/ml (n = 46); 37th-40th week: 3768 (2035-10691) pg/ml (n = 34); newborn cord serum 1608 (575-3095) pg/ml (n = 41).