Effect of large doses of morphine on experimental myocardial ischemia in cats.

The effect of large doses of morphine (1 mg/kg, i.v.) on experimental myocardial ischemia was evaluated in anesthetized open-chest cats. Myocardial ischemia was produced by intermittent coronary artery occlusion and assessed by measuring ST-segment elevation in multiple epicardial leads. The results obtained in the group of animals given morphine were compared with values obtained in animals given saline (control group), propranolol or nitrous oxide (reference groups). Morphine injected before coronary occlusion produced a significant increase in ST-segment elevation after left anterior descending coronary artery occlusion, whereas no significant change was noted in animals receiving normal saline or nitrous oxide. As expected, in the animals that received propranolol there was a pronounced decrease in ST-segment elevation. Our data suggest that large doses of morphine may increase myocardial ischemia when administered before coronary occlusion in the anesthetized open-chest cat.