Validation of the direct radioimmunoassay of prostanoids in serum and kidney.

Results obtained from radioimmunoassay (RIA) at various stages of sample processing were compared in order to determine the degree of purification necessary to estimate levels of prostaglandins (PG) and thromboxane B2 (TXB2). In serum, TXB2 levels were closely comparable when assayed directly or after organic extraction and thin layer chromatography (TLC). Although concentrations of 6-keto-PGF1 determined by both methods were correlated, levels were significantly overestimated by the direct method. PGE2 and 6-keto-PGF1 alpha levels measured directly in acetone extracted kidney homogenate were almost identical with kidney homogenates taken through the full extraction procedure and TLC. After indomethacin treatment serum 6-keto-PGF1 alpha and PG levels in kidney homogenate assayed directly were markedly different from extracted values. Thus direct RIA of samples is reliable when prostanoid levels are high in relation to interfering substances, as with serum TXB2 and kidney homogenate 6-keto-PGF1 alpha and PGE2, but not for serum 6-keto-PGF1 alpha or following PG inhibition.