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8-iso-PGF(2alpha) and 8-iso-PGE(2), which are released in vivo by free radical catalyzed peroxidation of arachidonic acid, are equipotent vasoconstrictors in vivo and in vitro. It is assumed that they exert this effect via activation of the thromboxane A(2) (TP) receptor or a TP-receptor-like isoprostane receptor. Increased levels of 8-iso-PGF(2alpha) have been detected in human cardiovascular diseases. It has been found that polyunsaturated fatty acids (PUFAs) have many beneficial effects in cardiovascular diseases, including antivasoconstrictor actions. Therefore, we investigated the influence of perfusions with eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA) and dihomo-gamma-linolenic acid (DGLA) at final concentrations of 3 and 30 micromol/l on vasoconstriction induced by 8-iso-PGF(2alpha), 8-iso-PGE(2) and the thromboxane A(2) mimetic U 46619 in the vasculature of the isolated perfused rabbit ear. Additionally, the effect of indomethacin (final concentration 3 micromol/l) on the effects of the PUFAs was investigated. Our results show that the PUFAs at a concentration of 30 micromol/l caused a significant inhibition of the vasoconstrictions induced by 8-iso-PGF(2alpha), 8-iso-PGE(2) and U 46619. Furthermore, it can be assumed that a part of the inhibitory effect of DGLA is due to the effect of a cyclooxygenase product, probably PGE(1), because indomethacin reduced the inhibitory effect of DGLA., (Copyright 2000 S. Karger AG, Basel.)

The isolated rabbit ear was prelabeled by perfusion with (1-14C)-eicosapentaenoic acid (EPA). Uptake and distribution in lipids, basal release and, in particular, stimulated release and metabolism was studied. In a series of experiments a comparison with results obtained by labeling the perfused organ with (1-14C)-arachidonic acid (AA) was made. Approximately 80% of the perfused labeled EPA was incorporated into the tissue. The main peak (74% of the incorporated radioactivity) was found in the phospholipids. Following incorporation of labeled EPA, basal release of EPA but ot of trienoic prostaglandins (PGs) could be observed. Bolus injection of bradykinin (3 micrograms) and the calcium-ionophore A23187 (10 micrograms) led to an immediate increased release of radioactivity in the effluent which declined within 10--20 min. Analysis of the extracted effluent by thin layer chromatography (TLC) showed that only the release of EPA and of radioactivity at the Rf-value of 12-L-hydroxy-5,8,10,14-eicosatetraenoic acid (HETE) was increased following stimulation by bradykinin and A23187. No labeled trienoic PGs could be detected. Upon injection of A23187 in the presence of indomethacin (3 micrograms/ml) there was no reduction of any peak of radioactivity on the TLC-plate, indicating that no cyclooxygenase product of EPA was generated. The extremely high dose of 10 micrograms bradykinin or 50 micrograms A23187 led to a small release of labeled PGI3 (A23187) and to a somewhat higher release of labeled PGE3 (bradykinin, A23187). In some experiments release and metabolism of labeled EPA were compared with those of labeled AA.(ABSTRACT TRUNCATED AT 250 WORDS)

The isolated rabbit ear was labeled by perfusion either with 14C-arachidonic acid (AA) or 14C-dihomo-gamma-linolenic acid (DGLA). The influence of unlabeled eicosapentaenoic acid (EPA) on the release and metabolism of the labeled prostaglandin (PG) precursors was studied with the aid of radio-thin-layer-chromatography (TLC). After incorporation of 14C-AA, the ionophore A 23187 (10 micrograms) stimulated the release of products comigrating on TLC plates with authentic PGI2 (measured as 6-keto-PGF1 alpha), PGE2, PGD2 and AA. In unlabeled ears, A 23187 (10 micrograms) stimulated the release of PGI2 and PGE2 (determined by radioimmunoassay) in similarly relative amounts as found for the labeled products. The release of PGD2 was not measured. After incorporation of 14C-DGLA, A 23187 (10 micrograms) stimulated the release of labeled products comigrating in several TLC-systems with 6-keto-PGF1 alpha (but not PGF1 alpha), PGE1, PGD1 and DGLA. After incorporation of 14C-AA, infusion of unlabeled EPA (0.1, 1 and 10 micrograms/ml) reduced the release of 14C-PGI2 but not of the other bisenoic PGs. Furthermore, in ears labeled with 14C-DGLA, EPA strongly reduced the release of a product comigrating with 6-keto-PGF1 alpha and to a lesser extent of a product comigrating with PGE1. Infusion of unlabeled EPA (1 and 10 micrograms/ml) did not reduce the release of 14C-AA or 14C-DGLA indicating that a phospholipase A2 was probably not inhibited by EPA. It is concluded that EPA inhibits PGI2 synthase rather than cyclooxygenase since after incorporation of 14C-AA, only the release of PGI2 is reduced.(ABSTRACT TRUNCATED AT 250 WORDS)

The isolated rabbit ear was perfused with 14C-arachidonic acid (AA), with 14C-eicosapentaenoic acid (EPA) or with 14C-dihomo-gamma-linolenic acid (DGLA). After incorporation of 14C-AA, the ionophore A 23187 (10 micrograms) stimulated the release of products comigrating with authentic PGI2 (measured as 6-keto-PGF1 alpha), PGE2 and PGD2 on the thin layer chromatography plate. After incorporation of 14C-EPA, A 23187 did not release any trienoic 14C-PGs. After incorporation of 14C-DGLA, A 23187 stimulated the release of labeled products comigrating with 6-keto-PGF1 alpha (but not PGF1 alpha), PGE1 and PGD1. Infusion of unlabeled AA (1 and 10 micrograms/ml) did not influence the metabolism of 14C-EPA or 14C-DGLA. Infusion of unlabeled DGLA (10 micrograms/ml) strongly stimulated the release of trienoic 14C-PGs but did not significantly increase the release of bisenoic 14C-PGs. Neither DGLA nor AA influenced the release of any other labeled incorporated PG precursor, indicating that a phospholipase A2 was not affected. The results show that DGLA is able to stimulate the metabolism of incorporated 14C-EPA resulting in an increased release of antiaggregatory trienoic PGs. The mechanism of this effect is unclear but it may be mediated via the formation of a hydroperoxide derivative of DGLA. Thus, an increased generation of antithrombotic trienoic PGs may be expected under special conditions, possibly also in vivo, depending on the supply of unsaturated fatty acids or the level of various hydroperoxide derivatives.