The effect of ouabain on pressor responses to infused noradrenaline in patients with essential hypertension.

The relationship between changes in the pressor response to infused noradrenaline induced by intravenous injection of ouabain, an Na+,K+-ATPase inhibitor, and plasma renin activity and plasma ionized calcium was examined in 16 normotensive subjects and in 16 patients with essential hypertension. These patients were divided into 11 normal-renin and five low-renin essential hypertensives. The pressor response was significantly greater in low-renin hypertensives than in normotensives and normal-renin hypertensives. Following the injection of ouabain, the pressor response was significantly increased with no change in basal levels of blood pressure, plasma noradrenaline concentration, plasma calcium and plasma parathyroid hormone in both normotensives and essential hypertensives. The pressor response to noradrenaline was negatively correlated with levels of plasma noradrenaline and calcium after the injection of ouabain as well as before the injection in normotensives and essential hypertensives. The regression line between the pressor response and that of plasma noradrenaline or plasma calcium was significantly shifted towards a higher pressor response in normotensives, but not in essential hypertensives. The changes in the pressor response to noradrenaline induced by the injection of ouabain was significantly smaller in essential hypertensives, particularly in low-renin hypertensives, compared with normotensives. These results suggest that: (1) ouabain increases the pressor response to noradrenaline; (2) this increase is related to calcium metabolism; (3) endogenous Na+,K+-ATPase inhibitor(s) might be elevated in essential hypertensives; and (4) an increase in endogenous Na+,K+-ATPase inhibitor might, therefore contribute to an enhanced noradrenaline response in essential hypertensives, particularly in low-renin hypertensives.