Vasoactivity of verapamil in the canine hindlimb and sympathetic nervous system interaction

Since enhanced sensitivity to verapamil in essential hypertension has been noted, a relationship between verapamil and the sympathetic nervous system has been suggested. It has also been noted that both verapamil and lumbar sympathectomy appear to decrease the vasospasm seen in Raynaud's phenomenon. To further investigate the possible interrelationship between verapamil and the sympathetic nervous system, a unilateral lumbar sympathectomy was performed on eight dogs. Two weeks later the femoral artery blood flow response to intra-arterial verapamil was compared on the sympathectomy limb side and the non-sympathectomy limb side. Blood flow measurements were done without surgical trauma by video dilution technique. Although baseline femoral artery blood flow was unchanged and equal on both sides following sympathectomy (4.6% of cardiac output), there was a significant rise, p less than 0.05, in the blood flow response to verapamil on the side of sympathectomy. Therefore, sympathectomy appears to enhance the calcium channel blocking properties of verapamil.