Correction of altered noradrenaline reactivity in essential hypertension by indapamide

Fourteen patients with untreated mild to moderate essential hypertension had, on average, an abnormally high cardiovascular reactivity to exogenous noradrenaline and angiotensin II, while plasma noradrenaline, renin activity, exchangeable body sodium, and blood volume were normal. Treatment with a low dose of indapamide (2.5 mg/day) for 6 weeks decreased blood pressure by 10% in these hypertensive patients but not in 13 normal control subjects. Plasma or blood volume and exchangeable sodium were not changed significantly; nevertheless, the latter, and body weight, tended to be decreased slightly. Though a mild reduction in extracellular sodium in both normal and hypertensive subjects appears possible, it may not fully explain per se the blood pressure-lowering effect of indapamide in essential hypertension. Indapamide induced a mild decrease in angiotensin II pressor responsiveness in normal or hypertensive subjects, but a possible depressor influence from this change was probably antagonized by a concomitant pronounced increase in plasma renin activity. In hypertensive patients, the abnormally high noradrenaline reactivity was corrected by indapamide without an accompanying increase in endogenous plasma noradrenaline levels. Indapamide-induced changes in blood pressure correlated with those in noradrenaline pressor dose. It was concluded, therefore, that indapamide may decrease blood pressure in essential hypertension at least in part by lowering an abnormally high cardiovascular noradrenaline reactivity without causing an equivalent increase in adrenergic nervous activity.