ROLE OF PGI(2) AND EPOXYEICOSATRIENOIC ACIDS IN RELAXATION OF BOVINE CORONARY-ARTERIES TO ARACHIDONIC-ACID

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 F1alpha (6-keto-PGF1alpha), 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-PGF1alpha. 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). 14,15-, 11,12-, 8,9-, and 5,6-EETs produced a concentration-related relaxation with an EC50 of approximately 10(-6) M and a maximal relaxation of 40-70% at 5 x 10(-6) M. These data suggest that the relaxation of the bovine coronary artery to arachidonic acid is mediated by PGI2 and epoxyeicosatrienoic acids.