| Abstract: | Direct cardiodepressant activities of three beta-blockers, carteolol, pindolol and propranolol, were estimated using heart-lung preparation of the dog. Beta-blocking doses of these drugs to inhibit the positive chronotropic effect of isoproterenol by 50% were 2.2 micrograms for carteolol, 4.0 micrograms for pindolol and 21 micrograms for propranolol. Cardiac performance of the preparation was not influenced by up to 1 mg of these three beta-blockers. After 10 mg of these drugs, the cardiac function curves were shifted rightward and downward indicating the heart failure. It was doubtful, however, that this result indicated the cardiodepressant action of beta-blockers, for the preparation showed spontaneous deterioration without beta-blocker treatment. The influences of these beta-blockers on the compromised heart-lung preparations showed essentially similar results. In conclusion, direct cardiodepressant activity of the beta-blocker, if any, was exerted with far more large doses than their beta-blocking doses. The implication of the results in clinical use of beta-blockers, especially in relation to heart failure, was discussed. |
