Evidence for the presence of two distinct types of antibodies in an antiserum raised against oestriol-16alpha-glucuronide

2- and 4-iodinated estriol as indicator ligands for estriol radioimmunoassays with anti-estriol-C6 conjugate antiserum

The suitability of 2- and 4-125I-estriol as indicator ligands for estriol determination in radioimmunoassays with anti-estriol-C6 conjugate antiserum was tested and compared to the one of 3H-estriol, estriol-6-(O-carboxymethyl)oxime-125I-histamine and a commercially available 125I-estriol derivative of unknown structure. An ideal radioiodinated tracer would react identically with the analyte and its tritiated analogue and the 4-monoiodo-estriol was found to fulfil these requirements as shown by the pattern of dilution and standard curves obtained with the various labeled ligands. This observation was corroborated by a comparison of the apparent estriol concentrations in human pregnancy sera determined with the different indicator ligands. The experimentally proven advantage of 4-monoiodo-estriol over other iodinated estriol derivatives verifies a hypothesis deduced previously from binding constants obtained with analogous estriol derivatives and the same antiserum.

A specific direct radioimmunoassay for oestriol-16alpha-glucuronide in pregnancy plasma

A specific radioimmunoassay has been developed for measuring oestriol-16alpha glucuronide in pregnancy plasma using a highly specific antiserum. The specificity of this antiserum has been assessed by the 50% displacement method and by measuring oestriol-16alpha-glucuronide concentrations in pregnancy plasma samples, both with and without chromatography. The antiserum was found to have Ka of 1.3 X 10(10) M-1. The assay had a sensitivity of 5 pg (least quantity of oestriol-16alpha-glucuronide distinguishable from the zero point, p less than 0.05), an intra-assay variation of 6.07% and an inter-assay variation of 3.36%. The assay was used to measure plasma oestriol-16alpha-glucuronide concentrations throughout eight pregnancies, five of which were normal and three had some defined abnormality.