EFFECTS OF ENALAPRIL ON THE HYPERINSULINEMIC RESPONSE TO SEVERE SALT RESTRICTION IN OBESE YOUNG MEN WITH MILD SYSTEMIC HYPERTENSION

Hypertension in obese patients is associated with hyperinsulinemia and salt sensitivity. Very low salt diets may exacerbate hyperinsulinemia, perhaps by activating the renin-angiotensin system. Therefore, the effects of a low salt diet alone and with enalapril on blood pressure and the insulin response to an oral glucose tolerance test were studied in 9 obese (body mass index 35 +/- 2 kg/m2) men with mild hypertension. Measurements were first obtained after a 2-week high-salt (20 mEq/day sodium diet + eleven 1 g salt tablets per day) baseline period. The same measurements were repeated after 2 weeks on a low salt diet (20 mEq/day) and after 2 weeks on low salt diet with enalapril in random sequence. The insulin area under the curve increased from 12.8 +/- 3.0 mU-min/dl during high salt to 16.6 +/- 3.2 mU-min/dl (p < 0.001). Plasma renin activity also increased with salt restriction from 1.4 +/- 0.2 to 3.0 +/- 0.5 ng/ml/hour, p = 0.01. With addition of enalapril to the low sodium chloride diet, the insulin area under the curve (14.5 +/- 2.6 mU-min/dl) was not significantly different from that during the high sodium chloride phase. Mean blood pressure in the laboratory was 105 +/- 1 mm Hg with high salt versus 99 +/- 1 mm Hg with low salt, p < 0.05. Addition of enalapril to the low-salt diet reduced mean blood pressure to 87 +/- 1 mm Hg (p < 0.01 vs low salt), largely by reducing total systemic resistance (p < 0.05). Salt restriction decreases laboratory BP while raising insulin levels in obese men with mild hypertension. Enalapril diminishes the hyperinsulinemic effect and enhances the hypotensive action of the low-salt diet. These findings indicate that the hyperinsulinemic effect of severe salt restriction persists for > 2 weeks. Moreover, activation of the renin-angiotensin system may contribute to impaired insulin metabolism during very low salt diets