Effects of verapamil on coronary vascular resistance in rabbits: Measurement with pulsed Doppler velocimetry

Background. Verapamil is an effective vasodilator. The purpose of this study was to investigate the in vivo effect of verapamil on coronary blood flow velocity and vascular resistance in anesthetized, open-chest rabbits. Methods. Twenty-one male New Zealand white rabbits were anesthetized, and a 3-mm suction-type pulsed Doppler velocimeter probe was applied to the proximal part of the left anterior descending coronary artery after median sternotomy. The rabbits received intravenous bolus infusion of 4 different doses of verapamil (0.01 mg/kg, n = 5; 0.1 mg/kg, n = 5; 1 mg/kg, n = 5, and 10 mg/kg, n = 6). The percent changes in coronary blood flow velocity and coronary vascular resistance were examined. Results. There was 10.0 ± 1.6% increase in coronary blood flow (CBF) and 12.5 ± 1.9% reduction in coronary vascular resistance (CVR) after infusion of 0.01 mg/kg of verapamil. The CBF increased 23.0 ± 9.5% and CVR decreased 24.2 ± 5.2% after infusion of 0.1 mg/kg of verapamil. Infusion of 1 mg/kg of verapamil induced 34.8 ± 10.5% increase in CBF and 32.6 ± 2.5% reduction in CVR. The CBF increased 41.1 ± 14.8% and CVR decreased 45.1 ± 5.4% after infusion of 10 mg/kg of verapamil. Conclusions. Compared with baseline condition, all doses of verapamil increased coronary blood flow velocity and decreased coronary vascular resistance significantly in anesthetized, open-chest rabbits.