Regional Hemodynamic Effects of a Digitalis Glycoside in the Conscious Dog with and without Experimental Heart Failure

The effects of intravenous ouabain (G-strophanthin), 20 µg/kg, on the superior mesenteric, renal, and external iliac beds were studied over a 30-minute period in eight normal conscious dogs before, and in five of them after, cholinergic blockade and in six conscious dogs with heart failure produced by tricuspid avulsion and progressive pulmonary stenosis. Blood flows were measured with Doppler ultrasonic and electromagnetic flowmeters. In normal dogs, prior to cholinergic blockade, ouabain caused early increases in mesenteric, renal, and external iliac resistances but later, between 15 and 30 minutes, mesenteric resistance decreased below the control level while renal and external iliac resistances remained elevated. After cholinergic blockade, the ouabain-induced alterations in renal and iliac resistance were unaltered, but the later decline in resistance in the mesenteric bed was reversed, resulting in sustained constriction. The late decline in mesenteric resistance also was not observed in the conscious animal after the injection of ouabain, 5 µg/kg, directly into the mesenteric artery or in the majority of dogs given ouabain intravenously after having been anesthetized with pentobarbital sodium. In the conscious dogs with heart failure, ouabain resulted in increased renal and iliac resistances initially, and in vasodilatation later while mesenteric resistance fell initially and remained below control for the entire 30 minutes. Thus, in the normal conscious dog, ouabain causes vasoconstriction in the regional vascular beds, apparently by its direct vascular action, and, in addition, a cholinergically mediated vasodilatation in the mesenteric bed. In the conscious dog with heart failure, ouabain increases blood flow to all beds, reducing the compensatory vasoconstriction of the low output state.