Previous studies have reported that polyunsaturated fatty acids (PUFAs) of nutritional interest may influence arachidonic acid (20:4n-6) metabolism in both platelets and endothelium, when tested separately. In the present study, platelets (PL) and cultured endothelial cells (EC) were first pre-enriched with eight different PUFAs for a two hour incubation in the presence of free fatty acid albumin pre-coated with each acid. EC, PL or both cell populations in combination, were then stimulated by thrombin (0.1 U/ml) for five minutes. Prostanoids were extracted, purified by thin-layer chromatography, and TxB2, 6-keto-PGF1 alpha and PGE2 were quantitated by radioimmunoassays. Prostanoids or dihomoprostanoids formed from cyclooxygenase substrates other than 20:4n-6 were measured by gas chromatography-negative chemical ionisation mass-spectrometry (GC-MS). When co-incubated with EC, PL produced less TxB2 (-15 and -85% in the absence and presence of thrombin, respectively). In contrast, 6-keto-PGF1 alpha increased by 189 (basal conditions) and 358% (thrombin stimulation) when PL were added to EC, in agreement with PGH2 transfers from PL to EC. PGE2, produced by both cell populations, reached amounts which roughly represent the sum of those measured in PL and EC alone, except when cells were pre-enriched with linoleic (18:2n-6) and the n-3 family fatty acids (18:3-, 20:5- and 22:6n-3). 6-keto-PGF1 alpha was markedly inhibited by adrenic acid (22:4n-6), while this acid was converted into dihomo-6-keto-PGF1 alpha, the stable metabolite of dihomoprostacyclin. 22:4n-6 also inhibited TxB2 formation and was converted into dihomo-TxA2.(ABSTRACT TRUNCATED AT 250 WORDS)