A Radioimmunoassay for Prostaglandin A1in Human Peripheral Blood*

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Abstract
A specific, sensitive and accurate radioimmunoassay (RIA) method for the measurement of prostaglandin A, (PGA1) in either human whole blood or plasma is described. Whole blood is immediately lysed with distilled water containing tritiated indicator. When plasma is assayed, the blood samples are handled at 4 C and rapidly centrifuged. The lysate or plasma is adjusted to pH 5 with buffer and quickly extracted with 5% methanol in dichloromethane. The whole blood or plasma extract is then purified by Sephadex LH20 chromatography using the system methanol: methylene chloride (5:95) which separates the major groups PGA, PGE and PGF. The RIA is then performed using an antiserum generated in rabbits from PGA1 coupled to bovine thyroglobulin. The antibody is highly specific, possessing very low cross reactivity to other prostaglandins (PGA2, PGE, PGB and PGF). Activated florisil or ammonium sulfate can be used to separate bound from free prostaglandin. This whole blood or plasma method yields blank values of only 2 ± 2 pg per sample with a between assay precision determined by duplicate analysis of 8% and interassay precision of 3%. The mean whole blood PGA1 concentration in 27 subjects is 2.5 ± 1.6 (sd) ng per 100 ml. No significant sex difference in PGA1 levels was noted and values were similar whether measured in whole blood or in cooled plasma rapidly prepared and extracted. These values of PGA1 are much lower than those RIA values reported by others for “PGA” using antibodies with lower specificities.

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