The effect of ouabain on nutritional circulation and regional myocardial blood flow

The effect of ouabain on myocardial nutritional circulation (rubidium-86 extraction) and regional myocardial blood flow (radioactive microspheres) was studied in the isolated supported canine heart preparation perfused at a constant coronary blood flow. Ouanbain (25 mug per kilogram, intravenously) produced a significant increase in mycocardial contractile force, peak left ventricular systolic pressure, and myocardial oxygen consumption. Ouabain also decreased rubidium-86 extraction (E86RB), rubidium-86 clearance (C86Rb), and the capillary transport coefficient (PS). Intracoronary infusion of ouabain (10 mug per minute) produced significant increases in contractile force (25,50, and 100 per cent above control), left ventricular systolic pressure, myocardial oxgen consumption, and the epicardial-endocardial blood flow ratio (epi/endo) of the left ventricle. When left ventricular systolic pressure was held constant (100 mm. Hg), ouabain infusion (10 mug per minute, intracoronary) increased myocardial contractile force (25,50, and 100 per cent above control) and myocardial oxygen consumption but did not change the epi/endo of the left ventricle. These results suggest that ouabain reduces E86Rb, C86Rb, and PS by producing a shunting of blood flow from endocardium to epicardium in the left ventricle. The increase in left ventricular systolic pressure appears to be responsible for these changes.