EFFECT OF DIETARY POTASSIUM ON BLOOD-PRESSURE, RENAL-FUNCTION, MUSCLE SYMPATHETIC-NERVE ACTIVITY, AND FOREARM VASCULAR-RESISTANCE AND FLOW IN NORMOTENSIVE AND BORDERLINE HYPERTENSIVE HUMANS

We evaluated the effect of a low potassium diet on blood pressure in normotensive (NT) and in borderline hypertensive subjects (BHT). There were 11 BHT men (age, 24.6 ± 1.2 years) and 10 NT men (age, 23.5 ± 1.0 years). Subjects were studied while on both low potassium, high sodium (30 meq/day, 400 meq/day) diets and high potassium, high sodium (100 meq/day, 400 meq/day) diets, each taken for 6 days. During the low potassium diet, daytime ambulatory systolic blood pressure increased in both NT (123 ± 5 mm Hg, low potassium, vs. 116 ± 4 mm Hg, high potassium, p < 0.01) and BHT groups (134 ± 3, low potassium, vs. 124 ± 3, high potassium, p < 0.001). Mean blood pressure was not different in NT during the two diets but was significantly higher during the low potassium diet in BHT subjects (97 ± 2 mm Hg low potassium, vs. 92 ± 1 mm Hg, high potassium, p < 0.05) without change in heart rate in BHT subjects during the two diets. Low potassium diet increased the postural rise in diastolic blood pressure when subjects changed from the supine position to quiet standing (standing diastolic blood pressure for NT: low potassium, 79 ± 2 mm Hg vs. high potassium, 72 ± 2 mm Hg; for BHT: low potassium, 89 ± 2 mm Hg vs. high potassium diet, 83 ± 2 mm Hg, p < 0.01). The effects of low potassium diet on blood pressure were not related to marked changes in renal hemodynamics, in plasma renin activity, in aldosterone, or in norepinephrine, nor to increases in forearm vascular resistance or in muscle sympathetic nerve activity. In fact, muscle sympathetic nerve activity decreased in the BHT group during low potassium compared with high potassium diets (p < 0.001) and did not change in the NT group. Sympathetic nerve activity was also higher in BHT compared with the NT group during high potassium and low potassium diets, p < 0.001. In the NT group, the low potassium diet was associated with lower hematocrit levels, weight gain, and increased 24 hour urinary calcium levels. After the low potassium diet, serum potassium fell in both groups, and serum phosphorus fell significantly in the BHT group. In BHT and NT groups after 5 days of low potassium diet, a water load was associated with enhanced natriuresis compared with the high potassium diet (NT: 390 ± 30 μeq/min, low potassium, vs. 280 ± 28 μeq/min, high potassium, p < 0.05; BHT: 364 ± 29 μeq/min, low potassium, vs. 326 ± 24 μeq/min, high potassium, p < 0.05). We conclude that a low potassium diet is associated with elevation in blood pressure and disturbances in several electrolytes in BHT and NT subjects. The elevation in blood pressure during a low potassium diet appears to be mediated in part by volume expansion.