Cyclooxygenase blockade limits blood flow to collateral-dependent myocardium during exercise

Cyclooxygenase blockade has been found to cause vasoconstriction of coronary collateral vessels in open-chest animals. This study was carried out to determine whether cyclooxygenase blockade can limit blood flow to collateral-dependent myocardium during exercise. Studies were performed in 8 adult mongrel dogs in which intermittent followed by permanent occlusion of the left anterior descending coronary artery produced an area of collateral-dependent myocardium. Myocardial blood flow was measured with radioactive microspheres at rest and during treadmill exercise to produce heart rates of 215 +/-0 7 beats/min. At rest collateral zone blood flow (1.00 +/- 0.10 ml/min per g) was significantly less than normal zone flow (1.23 +/- 0.14) (P < 0.05). During control exercise blood flow increased 91 +/- 22% in the collateral zone and 102 +/- 28% in the normal zone (each P < 0.05). Thirty minutes after cyclooxygenase blockade with indomethacin (5 mg/kg i.v.) blood flow in the normal zone and the collateral zone was not different from control during resting conditions. Indomethacin did not change heart rate or arterial pressure during exercise, but significantly increased the aortic-to-distal coronary pressure gradient from 33 +/- 3 to 40 +/- 5 mmHg (P < 0.05). Indomethacin increased transcollateral resistance during exercise by 42 +/- 10% (P < 0.05); this was associated with a 27 +/- 11% decrease in subendocardial flow in the collateral zone (P < 0.05) with no significant change in subepicardial flow, and no change in normal zone blood flow. These findings demonstrate that in the intact awake animal cyclooxygenase blockade causes coronary collateral vasoconstriction which can impair blood flow to the dependent myocardium during exercise.