Abstract
Effects of 2 different types of beta blockers, CS-359 and practolol, on mechanical performance and myocardial oxygen consumption (MVO2) in the isovolumic contraction of the isolated, blood-perfused canine heart with a support dog were studied. Two dose levels of the beta blockers were given intravenously to the support dog, one of which was enough to produce a significant beta adrenergic blocking action and other of which was a higher dose to reveal a direct depressant action on the isolated heart. CS-359 in the lower dose produced significant decreases in heart rate (HR), peak ventricular systolic pressure (peak VSP), and peak dp/dt while practolol caused no change in these parameters. The HR of the support dog was significantly decreased to the same degree in the lower dose of respective blocker. In the higher dose CS-359 decreased all parameters more definitely whereas practolol diminished peak VSP and peak dp/dt but did not significantly HR. MVO2 was decreased dose-relatedly by CS-359, but not affected significantly by practolol. From the analysis of relationships of MVO2 to peak VSP and HR in the isolated heart it is concluded that the effective reduction in MVO2 by CS-359 resulted mainly from a reduction in the peak VSP in the lower dose and additional decrease in HR in the higher dose of CS-359.
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