Effect of local infusion of ouabain on human forearm vascular resistance and on response to potassium, verapamil and sodium nitroprusside.

The effect of local infusion of ouabain into the forearm vascular bed has been examined in 15 normotensive male volunteers in an attempt to define the nature of the functional abnormalities of the resistance vessels in primary hypertension. Ouabain and other drugs were infused into the brachial artery and forearm blood flow was measured by venous occlusion plethysmography. Infusion of ouabain at 2 micrograms/min for 1 h caused a 26% reduction in forearm blood flow with a small rise in systemic arterial pressure; the increase in vascular resistance was unaffected by prior treatment with phentolamine. After infusion of ouabain the dilator response to potassium was reduced by 33% but the responses to verapamil and sodium nitroprusside were unchanged. The results show that acute depression of sodium pump activity by ouabain reproduces the increased resting resistance and impaired response to potassium that are seen in hypertension. It does not reproduce the relative enhancement of responsiveness to verapamil that is also observed in the resistance vessels of patients with hypertension and this abnormality must have some other cause.