Production of thromboxane and prostaglandins in human blood in the presence of thromboxane synthase inhibitors: a comparison of RIA and GC/MS determinations.

The radioimmunological determination (RIA) of primary prostaglandins (PGs) in serum and plasma was evaluated with gas chromatography/mass spectrometry (GC/MS). Human blood was stimulated in vitro in the presence or absence of the specific thromboxane synthase inhibitor ridogrel. TxB2, 6-keto-PGF1 alpha, PGE2, PGD2 and PGF2 alpha were determined with RIA and GC/MS on the same samples. For GC/MS analysis, prostanoids were extracted and derivatized to their methoximepentafluorobenzyl-esters-trimethylsilyl-ethers. An excellent correlation was observed between levels of all eicosanoids determined by RIA or GC/MS (r = 0.996-0.999) when plasma was spiked with known amounts of PGs and TxB2 (2-500 ng/ml). In stimulated blood, with or without inhibition of thromboxane synthase, the correlation between RIA and GC/MS values remained good, except for 6-keto-PGF1 alpha. RIA largely overestimated the levels of 6-keto-PGF1 alpha and no significant correlation was found with levels detected by GC/MS. The results demonstrate the importance of corroborating the reliability of RIA with GC/MS.