Radioimmunoassay of prostaglandins and thromboxane B 2 in extracted and unextracted urine and serum using an iodinated ligand

Abstract

A comparison of radioimmunoassay (R.I.A.) for 6-keto PGF 1α, PGE 2 and TXB 2 using 125I-histamine ligands and tritiated tracers showed a 7 to 10 fold increase in sensitivity for the 125I derivative, with a resultant reduction in antisera requirements by 80%. Study of the effect of purification of biological samples by organic extraction and thin layer chromatography showed that for human and rat urine, and urine from perfused rat kidneys, direct R.I.A. of unextracted samples gave substantially higher estimates of PGE 2 6-keto PGF 1α and TXB 2 than R.I.A. purified material. Indomethacin pre-treatment reduced the levels estimated in both extracted and unextracted samples; the results indicating that the higher estimates obtained by direct assay were due to a combination of PG/TXB 2 metabolites and non-specific interference. In serum from incubated human blood, estimated 6-keto PGF 1α and PGE 2 levels were significantly higher by direct R.I.A. than after extraction, whereas TXB 2 levels were similar. Thus purification procedures are unnecessary when high serum TXB 2 levels are being measured by R.I.A. with relatively specific antisera.