Effects of acute and chronic treatment with clonidine

The effect of clonidine on the relationship between sympathetic nervous system activity and the state of sodium-volume balance was studied in 15 patients with essential hypertension and normal renal function (group 1) and in 14 patients with hypertension and mild to moderate renal failure (group 2). Rapid administration of clonidine (200 micrograms) produced significant falls (p less than 0.01) in mean blood pressure, plasma levels of norepinephrine, plasma renin activity and aldosterone in both groups of patients. The changes in mean blood pressure were significantly correlated (p less than 0.01) with the changes in plasma norepinephrine. Chronic therapy with clonidine also produced significant falls in mean blood pressure and plasma norepinephrine, but not in plasma renin activity or aldosterone. Exchangeable sodium and plasma volume decreased significantly in patients of group 1 but not in patients of group 2. The data indicate that sympathetic nervous activity may be important for the abnormal relationship between pressure and natriuresis in subjects with essential hypertension and normal renal function, but not in hypertensive subjects with impaired renal function.