Radioimmunoassay of prostaglandins and thromboxane B2 in extracted and unextracted urine and serum using an iodinated ligand.

A comparison of radioimmunoassay (R.I.A.) for 6-keto PGF 1 alpha, PGE2 and TXB2 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 PGE2, 6-keto PGF1 alpha and TXB2 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/TXB2 metabolites and non-specific interference. In serum from incubated human blood, estimated 6-keto PGF1 alpha and PGE2 levels were significantly higher by direct R.I.A. than after extraction, whereas TXB2 levels were similar. Thus purification procedures are unnecessary when high serum TXB2 levels are being measured by R.I.A. with relatively specific antisera.