Effects of verapamil and nitroglycerin on coronary and systemic hemodynamics in conscious dogs

Effects of i.v. bolus administration of verapamil (10-300 micrograms/kg) and nitroglycerin (0.01-30 micrograms/kg) on coronary and systemic hemodynamics were studied in chronically instrumented conscious dogs. Verapamil in a dose of 10 micrograms/kg dilated the large epicardial coronary artery, increased the coronary blood flow and heart rate and decreased the aortic pressure. A reduction of left ventricular dP/dt was observed when over 30 micrograms/kg of verapamil was administered. Nitroglycerin in a dose of 0.01 micrograms/kg dilated the large epicardial coronary artery. Other variables such as coronary blood flow, aortic pressure and heart rate were influenced when over 0.1 micrograms/kg of nitroglycerin was given. The effects of these drugs on coronary and systemic hemodynamics were augmented when incremental doses were given. Duration of the increases in coronary diameter and coronary blood flow persisted longer after verapamil than after nitroglycerin. To estimate the changes in coronary diameter, independent of flow change, the effects of verapamil (100 micrograms/kg) and nitroglycerin (20 micrograms/kg) on the large epicardial coronary artery were reexamined when the coronary blood flow was maintained constant using a cuff occluder. The extent of coronary artery dilation, unaffected by coronary blood flow, was 62% with verapamil and 100% with nitroglycerin. Thus, although nitroglycerin preferentially and flow-independently dilates the large epicardial coronary artery, dilation of the large epicardial coronary artery after verapamil is augmented by the process of flow-induced arterial relaxation.