Ouabain-induced elevation in forearm vascular resistance, calcium entry and alpha-adrenoceptor blockade, and release and removal of noradrenaline.

The activity of the ouabain-sensitive Na+K+-ATPase may be reduced in primary hypertension by an ouabain-like humoral factor with resultant increase in intracellular Na+ and Ca2+ and peripheral vasoconstriction. To test this, we studied the forearm blood flow in 18 normotensive subjects. First, nifedipine, phentolamine, prazosin, sodium nitroprusside and ouabain were infused into the brachial artery. Secondly, each vasodilator was given in combination with ouabain. Blood pressure was measured directly, and blood flow by venous occlusion plethysmography. When nifedipine was combined with ouabain the elevation of vascular resistance was completely abolished. We detected no effect on the forearm veno-arterial difference for noradrenaline following intra-arterial infusion of drugs. If an ouabain-like factor plays a role in producing the elevated resistance of chronic hypertension, calcium entry blockers will act close to the site of this primary abnormality.