Abstract
The relevance of changes in substrate and ion transport to left ventricular contractility alterations have been examined after insulin, strophanthidin, and their combination, using serial arterial-coronary sinus differences in intact anesthetized dogs. Insulin (0.1 U/kg) was infused into a left coronary artery catheter to minimize systemic changes, producing an accumulated left ventricular uptake of glucose, lactate, and potassium with a rise in respiratory quotient, without affecting pyruvate and free fatty acid extractions. There was no associated change in the d p/d tmax. of left ventricular pressure or in the duration of isometric contraction, used as indices of contractility. Acetyl strophanthidin, .03 mg/kg, produced a 60% increase in d p/d tmax. and significantly shortened isometric duration associated with egress of potassium from the myocardium. Insulin, given 25 min before strophanthidin to reduce K+ egress, failed to do so, but largely interfered with its contractile properties. This effect was also observed with p-chloromercuribenzoate, so that a SH-binding site would seem essential for the inotropic activity of strophanthidin.
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