THE EFFECT OF CORONARY VASODILATATION (DIPYRIDAMOLE-INDUCED) ON THE MYOCARDIAL DISTRIBUTION OF TRITIATED WATER

The uptake of tritiated water in the left ventricle has been studied during constantly increasing concentrations of tritium in two groups of normal dogs, one of which received dipyridamole intravenously while the other acted as control. Dipyridamole administration was associated with a 1.6 times greater coronary flow and an appropriate reduction in arterial coronary sinus oxygen difference. As judged by the concentrations of indicator in different myocardial samples the perfusion of the myocardium of the normal dog is relatively homogeneous. No differences were detected between the inner and outer half of the ventricular wall or between the apical region and the free wall of the left ventricle. Comparison of myocardial and coronary sinus concentrations of tritium indicated that the increased coronary flow following dipyridamole was the result of an increase in the effective capillary flow rather than a shunting through diffusion-limited pathways, such as would occur in functional or anatomical arterio–venous shunts.