1. Using a Mulvany-Halpern myograph to measure changes in isometric tension, we have investigated the effect of ouabain on noradrenaline-induced contraction of human subcutaneous resistance arteries.
2. Low concentrations of ouabain (10 nmol/l or less) were shown not to alter vascular smooth muscle contractility or sensitivity to noradrenaline.
3. In contrast, higher concentrations of ouabain (100 nmol/l or more) were found to depress vascular smooth muscle contractility and to reduce the sensitivity of the noradrenaline concentration-response relationship.
4. These findings may have implications regarding the presence of an endogenous inhibitor of the sodium pump in essential hypertension and in pregnancy-associated hypertension.