Effects of nitroglycerin, dipyridamole and propranolol on myocardial pH and pO2 during regional ischemia in the dog heart.

In dogs anesthetized with pentobarbital, the left anterior descending coronary artery (LAD) was occluded so that the blood flow could be reduced to about 1/3 (partial occlusion). Before partial occlusion, myocardial pH and pO2 were 7.63 (n = 35) and 17.1 mm Hg (n = 30), respectively. Partial occlusion of the LAD decreased the pH and pO2 by 0.68 pH units and 7.4 mm Hg, respectively. In the nonischemic heart, nitroglycerin (20 micrograms/kg, i.v.) did not affect myocardial pH, although it increased the LAD flow. In the ischemic heart, however, nitroglycerin increased the myocardial pH that had been reduced by partial occlusion, without an increase in myocardial pO2. Dipyridamole (250 micrograms/kg, i.v.) did not increase pH and pO2 in both nonischemic and ischemic hearts. Propranolol (1 mg/kg, i.v.) increased both pH and pO2 of the ischemic myocardium that had been reduced by partial occlusion with a decrease in heart rate. It is concluded that propranolol and nitroglycerin restore (though incompletely) the myocardial pH that has been reduced by partial occlusion of the coronary artery, while dipyridamole does not, and that only propranolol increases the ischemic myocardial pO2.