Determination of peripheral plasma prostanoid concentration: an unreliable index of 'in vivo' prostanoid activity.

Plasma concentrations of PGE2, PGF2 alpha, 6-keto-PGF1 alpha and TxB2 were determined in 4 healthy volunteers by gas chromatography-negative ion chemical ionization mass spectrometry. TxB2 concentrations in all volunteers increased with time during blood collection, increases occurred more sporadically in the case of PGE2, PGF2 alpha and 6-keto-PGF1 alpha. Rapid changes in plasma prostanoid concentrations within a sampling series were unpredictable and were inexplicable. The measured plasma prostanoid concentrations apparently depended on the sampling conditions, which could not be adequately standardized and controlled. However, very short term changes in plasma prostanoid levels cannot be excluded.