The influence of verapamil on dopamine's ability to augment cardiac output

Calcium channel blockers are used in the treatment of angina pectoris, cardiac arrhythmia, and hypertension. Sporadic reports of hypotensive reactions to verapamil have indicated that these reactions are not reversed readily by catecholamine administration. This study was conducted to test the hypothesis that verapamil pretreatment does not alter the ability of dopamine in conventional doses to augment cardiac output. Twelve mongrel dogs, weighing 19 to 25 kg, were anesthetized with pentobarbital and placed on a respirator. Heart rate, cardiac output, and the right atrial, pulmonary artery, pulmonary capillary wedge, and central aortic pressures were measured directly. Dopamine, 10 micrograms/kg/min, increased cardiac index by 52.4 mL/kg/min over baseline. The dopamine was stopped and the animals were allowed to return to baseline. Dopamine, 10 micrograms/kg/min, was administered again after pretreatment with 0.15 mg/kg verapamil, and it increased cardiac index by 47.9 mL/kg/min over the second baseline control. The results were not statistically different using the Student t test for paired data (P greater than .05). It is concluded that verapamil does not affect dopamine's ability to augment cardiac output in the dosages tested.