Re-examination of the assay for plasma prostanoids by solid-phase extraction, and radioimmunoassay

A method for the routine assay of plasma thromboxane and prostacyclin metabolites, thromboxane B 2 and 6ketoprostaglandin F 1α (employing solid phase extraction to remove the metabolites from interfering substances) and using commercially available antisera for their radioimmunoassay has been investigated. Modifications of previously published procedures have been explored, including the use of non-explosive solvents in the extraction procedure, and inclusion of a non-cross reacting internal standard, prostaglandin D 2, to estimate recovery through the extraction procedures. Both the original and modified procedures can produce high blank values, which apparently result from the solid-phase extraction. These high backgrounds are constant for a given lot of solid phase extraction cartridges and can be corrected by subtraction. The modified method is linear with volume of plasma assayed to as little as one ml, and all cross-reacting material in normal human plasma was found to co-chromatograph with authentic standards on reverse-phase high performance liquid chromatography. Values for normal adult plasmas were found to be 0.44 ±.15 pmol/ml 6keto PGF i1α (mean ± SD) and .103±.07 for thromboxane B 2. The method reported provides a convenient, reproducible way to assay these important plasma prostanoids.