Effects of nitroprusside on myocardial blood flow in acute regional coronary ischaemia in conscious dogs with and without left ventricular distension.

To determine the effects of nitroprusside on regional myocardial ischaemia, experiments were done in 11 conscious dogs with balloon-cuff occluders implanted around the left anterior descending coronary artery (LAD). Regional myocardial blood flow by the microsphere method was determined during 5 min periods of temporary LAD occlusion with and without nitroprusside infusion. Nitroprusside decreased aortic mean and left ventricular diastolic pressures. Blood flow increased to ischaemic myocardium supplied by the occluded LAD and to non-ischaemic myocardium supplied by the patent left circumflex coronary artery. Experiments were repeated on a separate day in the presence of left ventricular distension in the same dogs. Nitroprusside again decreased aortic mean and left ventricular diastolic pressures and increased the blood flow to both ischaemic and non-ischaemic myocardial regions. These results suggest that nitroprusside can improve perfusion to acutely ischaemic myocardial tissue despite a fall in aortic pressure, presumably by decreasing resistance to flow in coronary collateral vessels or by decreasing the myocardial tissue pressure.