CHICAGO — For the first time, researchers have shown that reducing salt intake can protect against aldosterone-induced reduction in blood vessel flexibility in patients with resistant hypertension.
The research also suggests that measuring urinary aldosterone and sodium may help predict cardiovascular risk in patients with resistant hypertension, David A. Calhoun, M.D., reported in a poster presentation at a conference of the Council for High Blood Pressure Research.
In a study of 120 consecutive patients with resistant hypertension (uncontrolled by three or more medications) whose dietary salt intake was not restricted, Dr. Calhoun and colleagues prospectively evaluated plasma renin activity and 24-hour urinary aldosterone and sodium excretion.
Brachial artery flow-mediated dilation (FMD) also was measured prospectively in all patients by using high-resolution ultrasound. The ability of an artery to relax and expand in response to increases in blood flow is a sign of a flexible artery with a healthy endothelium. FMD is the percentage of change in vessel diameter after a tourniquet placed on the forearm is released.
Aldosteronism, defined as suppressed plasma renin activity less than 1.0 ng/mL per hour and elevated aldosterone excretion, defined as greater than 12 mcg/24 hours, was found in 34 patients, said Dr. Calhoun of the vascular biology and hypertension program at the University of Alabama, Birmingham.
In the aldosteronism patients, there was a strong negative correlation between FMD and urinary sodium excretion (correlation coefficient -0.39), as well as the product of urinary aldosterone and sodium (correlation coefficient -0.46), consistent with better endothelial function in patients eating a lower-sodium diet.
The patients were divided into low- or high-sodium groups based on urinary sodium excretion of less than or greater than 150 meq/L per day. Mean FMD was higher in the 10 patients with low urinary sodium excretion than in the 24 patients with a high sodium excretion (2.6% vs. 1.6%, respectively). The groups were similar in age, body mass index, mean blood pressure, medication use, and aldosterone excretion.
In the five patients with very low sodium excretion (less than 100 meq/L per day), FMD was even higher (3.4%). This is consistent with a dose-dependent relation between sodium excretion and endothelial function, Dr. Calhoun concluded at the meeting, sponsored by the American Heart Association.