Metabolites of arachidonic acid regulate several physiological processes, including vascular tone. The purpose of this study was to determine which metabolites of arachidonic acid are produced by bovine coronary arteries and which may regulate coronary vascular tone. Arachidonic acid induced a concentration-related, endothelium-dependent relaxation [one-half maximum effective concentration (EC50) of 2 x 10(-7) M and a maximal relaxation of 91 +/- 2% at 10(-5) M] of bovine coronary arteries that were contracted with U-46619, a thromboxane mimetic. The concentration of 6-ketoprostaglandin F1 alpha (6-keto-PGF1 alpha), a metabolite of prostaglandin I2 (PGI2), increased from 82 +/- 6 to 328 +/- 24 pg/ml with arachidonic acid (10(-5) M). Treatment with the cyclooxygenase inhibitor indomethacin attenuated arachidonic acid-induced relaxations by approximately 50% and blocked the synthesis of 6-keto-PGF1 alpha. PGI2 caused a concentration-related relaxation (EC50 of 10(-8) M and a maximal relaxation of 125 +/- 11% at 10(-7) M). BW755C, a cyclooxygenase and lipoxygenase inhibitor, inhibited arachidonic acid-induced relaxation to the same extent as indomethacin. When vessels were treated with both indomethacin and BW755C, the inhibition of relaxation was the same as either inhibitor alone. SKF 525a, a cytochrome P-450 inhibitor, reduced arachidonic acid-induced relaxation by approximately 50%. When SKF 525a was given in combination with indomethacin, the relaxation by arachidonic acid was almost completely inhibited. SKF 525a inhibited the synthesis of epoxyeicosatrienoic acids (EETs).(ABSTRACT TRUNCATED AT 250 WORDS)

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The goal of the present study was to demonstrate that intracoronary platelet deposition may trigger intense vasoconstriction of large epicardial coronary arteries in vivo and that this is largely mediated by thromboxane A2 and serotonin released by activated platelets. Cyclic flow variations (progressive declines in blood flow followed by sudden restorations of flow) due to recurrent intracoronary platelet activation and thrombus formation were induced by damaging the endothelium and placing a cylindrical constrictor on the left anterior descending coronary artery (LAD) in open-chest, anesthetized dogs. Coronary diameters were measured in vivo by means of ultrasonic crystals sutured on the LAD immediately distal to the constrictor (LADI) and 1 cm below (LAD2) and on the circumflex coronary artery (Cx). Coronary artery diastolic diameters were measured continuously before and during cyclic flow variations and after they were abolished by administration of LY53857, a serotonin-receptor antagonist (group 1, n =7), or SQ29548, a thromboxane-receptor antagonist (group 2, n = 7). During cyclic flow variations, at the nadir of coronary flow, LADI (a site of maximal platelet accumulation) cross-sectional area decreased by 52±10% and 38±6% in group 1 and 2 animals, respectively (p <0.001 compared with values recorded during a brief LAD occlusion obtained by a suture snare), whereas LAD2 (a site of minimal or no platelet accumulation) cross-sectional area did not differ from that recorded during the brief LAD occlusion. SQ29548 abolished cyclic flow variations in seven of seven dogs and LY53857 in six of seven, but they affected the increased coronary vasoconstriction differently: LADI cross-sectional area increased by 32±N6% of the control value in SQ29548-treated animals, whereas it returned to baseline dimension values in the LY53857-treated group as these interventions also abolished the cyclic flow variations. We conclude that a marked coronary vasoconstriction may be triggered by local platelet deposition and that thromboxane A2 and serotonin are mediators of this vasoconstriction. (Circulation 1989;79:154-166) It is currently believed that the pathophysiology of unstable angina is a primary reduction in coronary blood flow.

Coronary vascular injury promotes blood cell-vessel wall interactions that influence arachidonic acid metabolism and coronary blood flow patterns. Since lipoxygenase and cytochrome P-450 epoxygenase metabolites of arachidonic acid are synthesized by vascular and inflammatory cells and have a variety of important biological actions, we investigated the metabolism of arachidonic acid by these pathways in normal and stenosed, endothelially injured canine coronary arteries. We found and confirmed by gas chromatography/mass spectrometry that primarily 12- and 15-hydroxyeicosatetraenoic acids (HETEs) are synthesized by both coronary artery segments. Lesser amounts of 11-, 9-, 8-, and 5-HETEs are also produced. 15-Ketoeicosatetraenoic acid is also synthesized. The synthesis of 14C-HETEs is fivefold to 10-fold greater by the stenosed than the normal coronary artery. Specific radioimmunoassays indicated that the stenosed coronary artery synthesized 93 +/- 14 and 1,102 +/- 154 ng/g of tissue of 15- and 12-HETE, respectively, while the normal coronary artery produced 17 +/- 3 and 162 +/- 68 ng/g of tissue of 15- and 12-HETE, respectively. Products comigrating with 14,15-; 11,12-; 8,9-; and 5,6-epoxyeicosatrienoic acids (EETs) and the corresponding dihydroxyeicosatrienoic acids (DHETs) were detected predominantly in stenosed coronary arteries by high-pressure liquid chromatography. The structures of the EETs were confirmed by GC/MS. The EETs and prostaglandin I2 produced endothelium-independent, concentration-related relaxations of dog coronary artery rings. These data indicate that normal and stenotic coronary arteries metabolize arachidonic acid to HETEs, DHETs, and EETs along with prostaglandins; however, the synthesis of these metabolites is greater in the stenosed, endothelially injured vessel. The EETs may be synthesized during the development of cyclic flow variations and counteract the vasoconstrictor effects of thromboxane A2.

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