NEUROHUMORAL AND METABOLIC EFFECTS OF SHORT-TERM DIETARY NACL RESTRICTION IN MEN - RELATIONSHIP TO SALT-SENSITIVITY STATUS

Published observations suggest that not everyone benefits from severe dietary NaCl restriction, since blood pressure responses appear heterogeneous and adverse metabolic effects may occur. We studied the cardiovascular, neurohumoral, and metabolic effects of 7 day periods of 20 v 200 mEq/day NaCl diets in 27 men. Twelve subjects were salt sensitive (SS), defined as mean intraarterial pressure (MAP, mm Hg) during high NaCl greater-than-or-equal-to 5% above MAP on low NaCl. Eleven subjects were salt resistant (SR), defined as MAP during the low NaCl phase greater-than-or-equal-to MAP during the high NaCl phase. The SR subset had a tendency to greater neurohumoral activity, assessed by changes in mean values for plasma norepinephrine (NE, P = .12) and plasma renin activity (PRA, P < .001) on the low v high NaCl diet. In SR subjects the low v high NaCl diet also raised mean values for creatinin (P = .03), uric acid (P = .001), and low density cholesterol (LDL-C, P = .03), but not fasting insulin (P = .15). In SS subjects, the low v high NaCl diet did not raise NE (P = .35), although the PRA was greater (P = .002). Among SS subjects, mean values for uric acid (P = .005) and insulin (P = .02) were greater during the low v high NaCl phase, while creatining (P = .15) and LDL-C (P = .67) were not different. The data sugges that severe, short-term NaCl restriction can be undesirable, especially in SR subjects, since potentially adverse neurohumoral and metabolic changes are not counterbalanced by the benefits of a lower MAP.