Hemodynamic effects of practolol at rest and during exercise.

SUMMARY The effects of practolol, a new beta-adrenergic blocking agent, and propranolol were studied in volunteers. At rest, practolol caused a very small reduction in cardiac index (CI), 190 ml, P < 0.25, and preejection period (PEP) lengthened 3 msec, P < 0.025. In contrast, propranolol caused a reduction in CI of 770 ml, P < 0.001. Heart rate (HR) slowed 10 beats/min, P < 0.001, stroke volume index (SVI) fell 6 ml, P < 0.005, PEP lengthened 16 msec, P < 0.001, and peripheral vascular resistance (PVR) increased 419 dynes-sec-cm-5, P < 0.001. Practolol reduced the increase in CI caused by an isoproterenol infusion by 65%, P <0.005, by blocking the increase in HR by 73%, P < 0.05. Practolol also reduced the shortening of PEP and LVET caused by isopro-terenol. PVR decreases due to isoproterenol were not blocked by practolol although they were slightly attenuated, P < 0.025. Practolol reduced the increase in CI caused by exercise by 22%, P < 0.05, by blocking the increase in HR by 29%, P < 0.01. Practolol also reduced the increase in tension-time index due to exercise by 25%, P <0.025. Practolol has little effect on the performance of the normal heart at rest. It does block the cardiac effects of isoproterenol and exercise, largely through chronotropic mechanisms. The reductions in pressure-time relationships with exercise indicate reduced oxygen consumption by the heart, and therefore imply a therapeutic benefit in exercise-induced angina. Additional Practolol Exercise Indexing Words: Peripheral vascular resistance Angina pectoris Isoproterenol ECENTLY several cardiac sympathetic blocking agents have been developed that appear to have limited adverse effects on resting cardiac performance in animals. Prac-tolol is one of these new beta-adrenergic blocking agents. Extensive animal studies have shown that small dose levels of practolol attenuate the effects of isoproterenol on heart rate and contractility, and at very large dose 46 Propranolol Tension-time index levels impairment of resting ventricular performance occurs while coronary blood flow increases. The effects of isoproterenol on peripheral vascular resistance are not blocked by practolol. It was not possible to assess the potency ratio of practolol and propranolol in these studies because the slope of their dose-response curves for heart rate and cardiac contractile force is different.1 3 These animal data do indicate that practolol in low and intermediate dose ranges is one-fourth as effective as propranolol in terms of its ability to block isoproterenol-induced tachycardia. Brick and …