Effect of cyclooxygenase inhibition on the adaptation of coronary blood flow to tachycardia

Background. The role of different endothelium-derived vasoactive substances in the regulation of coronary circulation during tachycardia is not well d efined. In order to elucidate the contribution of prostacyclin to the adapt ation of coronary blood flow to tachycardia, the effect of meclofenamate, a cyclooxygenase inhibitor on the coronary blood flow response to rapid atri al pacing was analyzed in a porcine model. Methods. A group of seventeen pigs were instrumented for coronary blood flo w, aortic pressure and atrial pacing. Heart rate was increased by 20 beats every 5 minutes. Coronary blood flow and aortic pressure were measured, and coronary resistance calculated, basally and at each pacing interval, befor e and after saline serum (n = 6), meclofenamate 5 mg/kg, i.v. (n = 7) or me clofenamate 35 mgikg, i.v. (n = 4). Results. Neither saline nor meclofenamate modified the normal increase of c oronary blood flow provoked by rapid atrial pacing (163 +/- 28% increase be fore versus 172 +/- 29% after saline; 159 +/- 21% increase before versus 16 1 +/- 22% after meclofenamate low dosis and 201 +/- 39% before vs 172 +/- 3 6 after meclofenamate high dosis). There were no differences in the respons e of coronary vascular resistance to tachycardia before and after meclofena mate (44% reduction vs 40% respectively). Conclusion. Cyclooxygenase blockade does not modify the response of coronar y circulation to rapid atrial pacing, suggesting that prostacyclin does not play a limiting role in the regulation of coronary blood flow during tachy cardia in this model.