Facile radioimmunoassay of estradiol 3-sulfate in plasma during pregnancy.

A facile, sensitive radioimmunoassay of estradiol 3-sulfate in pregnancy plasma was established. Highly specific antisera were raised in male rabbits against a conjugate of 6-oxoestradiol 3-sulfate-(O-carboxymethyl)oxime with bovine serum albumin. After purification of the antiserum, we coupled the crude globulin fraction to CNBr-activated Sepharose-4B and used this for direct radioimmunoassay of estradiol 3-sulfate in plasma without sample pre-treatment such as solvent-extraction or chromatography to remove endogenous interferences. Using this assay system, we determined concentrations of estradiol 3-sulfate in plasma from pregnant women. Concentrations of estradiol 3-sulfate in plasma increased in proportion to those of estradiol throughout gestation, but were about twice as high as those of unconjugated estradiol at each week of pregnancy.