EFFECT OF SODIUM-INTAKE ON INSULIN SENSITIVITY

To examine the effects of sodium intake on insulin sensitivity, we per formed euglycemic insulin clamp studies (40 mU.m-2.min-1) in eight hea lthy normotensive nondiabetic white males (age = 36 +/- 5 yr; wt = 66 +/- 3 kg) after 5 days on high (200 meq/day)- and low (10 meq/day)-sod ium diets administered in random order. High sodium intake was associa ted with significantly greater urinary sodium excretion (160 +/- 7 vs. 8 +/- 2 meq/day; P < 0.0001), suppression of plasma aldosterone (7 +/ - 3 vs. 38 +/- 6 ng/dl; P < 0.001) and renin (1.5 +/- 0.2 vs. 6.0 +/- 0.9 ng.ml-1.h-1; P < 0.005) levels, but no change in blood pressure (1 16 +/- 3/63 +/- 2 vs. 114 +/- 3/64 +/- 2 mmHg; P = not significant). T he rate of glucose infusion during the clamp was significantly reduced during the high- vs. low-sodium diet (279 +/- 19 vs. 334 +/- 24 mg.m- 2.min-1; P < 0.01). This impairment in insulin sensitivity was not rel ated to changes in serum potassium, epinephrine, norepinephrine, corti sol, or growth hormone but was highly correlated with an increment in circulating free fatty acid levels during high sodium intake (r = 0.82 , P < 0.05). These data suggest that 1) high sodium intake may exacerb ate insulin resistance by increasing circulating free fatty acids, and 2) differences in sodium intake may influence measures of insulin sen sitivity in other disease states.