Salt sensitivity in human essential hypertension: effect of renin-angiotensin and sympathetic nervous system blockade.

We studied the acute effect of oral captopril (25mg) and clonidine(300 micrograms) on blood pressure (BP) in patients with essential hypertension successively maintained on a low (LSD) and high (HSD) salt diet. Seven patients were salt sensitive (SS) and seven were salt resistant (SR). The maximal decrease in diastolic BP caused by captopril in patients on the LSD was greater in SS than SR individuals. Baseline urinary norepinephrine levels did not change from LSD to HSD (p greater than 0.05) in SS patients and decreased in SR patients (p less than 0.05). The maximal decrease in mean BP during the clonidine test was the same for both diets (p greater than 0.05) in SS patients and was lower (p less than 0.05) for the HSD in SR patients. SS patients on the HSD presented a higher decrease in systolic BP than SR patients (p less than 0.05) during the clonidine test. These data suggest overactivity of the renin-angiotensin system in SS patients on the LSD and of the sympathetic nervous system in SS patients on the HSD and that the clonidine test could be a good indicator for identifying SS and SR patients.