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Femoral arterial blood pressure and electrocardiograms (ECG, lead II) were recorded concurrently in artificially respired cats anesthetized with pentobarbital, and responses to the new squill glycoside, proscillaridin (Talusin), and to ouabain were compared. All drugs were injected intravenously, in groups of five cats for each dose level. Following single injections, it was observed that doses of 150 μg of proscillaridin/kg produced only slight increases in blood pressure and slight bradycardia, but no change in the ECG pattern. In contrast, similar doses of ouabain or doses of 500 μg of proscillaridin/kg produced bradycardia, ventricular arrhythmias, and fibrillation in all experiments. Whereas striking pressor effects were noted with ouabain those due to proscillaridin were slight. With continuous infusions, proscillaridin and ouabain in doses of 5 μg/kg per minute led to similar qualitative and quantitative changes (bradycardia, arrhythmias, and ventricular fibrillation), but these developed more slowly with proscillaridin. Infusions of proscillaridin in doses of 2.5 μg/kg per minute also produced similar but still more delayed changes. Doses of 15 μg/kg per minute of proscillaridin, on the other hand, produced all the effects more rapidly than 5 μg/kg per minute of ouabain, but the pressor response was again less pronounced. It is concluded that (a) proscillaridin exerts characteristic digitalis-like effects; (b) when single intravenous doses are compared, proscillaridin is approximately one-third as toxic to the heart as ouabain; (c) when continuous intravenous infusions are compared, proscillaridin shows variable onset of action depending on dosage and is approximately one-half as toxic as ouabain; and (d) in all experiments proscillaridin exerts less marked pressor effects than ouabain. The drug is being further studied.

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