THE EFFECT OF SODIUM-INTAKE ON VENTRICULAR PERFORMANCE IN HEALTHY-MEN

We analyzed the effects of acute sodium intake on left ventricular performance in 11 healthy normotensive men using Doppler echocardiography. For 2 weeks, they took 2,700-kcal diets containing 6 g and 24 g sodium chloride per day in the low sodium phase (5 days) and in the high sodium phase (5 days), respectively. Blood pressure, urine, hematocrit, and echocardiographic values were measured every day throughout this study. Although a decrease in the serum norepinephrine concentration and an increase in the ejection fraction were noticed in the low sodium phase, there was no significant change in the relation between end-systolic stress and mean velocity of circumference shortening. All subjects also performed a cold pressor test in both phases, and we analyzed the end-systolic stress-volume relation (modified E(max)). Modified E(max) of the high sodium phase was significantly larger than that of the low sodium phase. As published in previous research on dogs, we consider that this discrepancy at rest may be caused by a dysfunction at the cardiac adrenergic neuroeffector junction in humans, too, and that sodium intake may enhance the change in ventricular contractility by a cold pressor test.