Effects of a Digitalis Glycoside on Coronary and Systemic Dynamics in Conscious Dogs

The effects of ouabain (G-strophanthin), 20 μg/kg were compared in 12 conscious dogs with Doppler flow transducers on the ascending aorta and left circumflex coronary artery and pressure gauges in the aorta, and in 9 of these dogs after general anesthesia with Na pentobarbital. In conscious dogs ouabain caused an initial bradycardia, but heart rate returned almost to control at 15 to 30 minutes, while arterial pressure rose and remained elevated. Cardiac output and coronary blood flow decreased initially, returned to control by 5 minutes and then remained constant. Systemic, mean, and late diastolic coronary resistances were elevated within 1 minute and remained elevated for 30 minutes. After anesthesia, ouabain caused similar increases in arterial pressure and slightly greater increases in systemic resistance, but the bradycardia and reduction of cardiac output were more profound and sustained. In the anesthetized state, coronary resistance rose when heart rate was allowed to slow after ouabain but was not elevated when heart rate was returned to control. Thus, in the conscious state, ouabain caused a distinct elevation in coronary and systemic resistances with no change in cardiac output, while in the anesthetized state ouabain reduced cardiac output and when heart rate was controlled, did not alter coronary resistance.