Radioimmunoassay techniques for the determination of the local release of prostaglandins and thromboxanes.

Radioimmunoassay techniques are described that enable the quantification of the local release of prostaglandin (PG) E2, PGF2 alpha, TxB2 (the metabolite of thromboxane A2), and 6-keto PGF1 alpha (a metabolite of prostacyclin) from various organs in vivo. Plasma samples were acidified and the prostanoids extracted with ethyl acetate, prior to assay. The mean recovery of tritiated internal standards was 60% for 6-keto PGF1 alpha and 84% for the other prostanoids. Sample extracts were redissolved in phosphate-buffered saline and the appropriate tritiated antigen and specific antibody were added. After overnight incubation the antibody-bound and free prostanoid were separated using dextran-coated charcoal. The intraassay variation and the interassay variation were similar for all prostanoids; the mean values being 8.5% and 13.2%, respectively. There were variations in the sensitivity of the radioimmunoassay for each prostanoid. Using 250 microliter plasma samples the detection limit for PGE2 was 75 pg/ml, PGF2 alpha 50 pg/ml, TxB2 25 pg/ml, and 6-keto PGF1 alpha 125 pg/ml. These assays have been used to determine prostanoid concentrations in rats, cats, dogs, and humans.