RENIN AND ALDOSTERONE ARE HIGHER AND THE HYPERINSULINEMIC EFFECT OF SALT RESTRICTION GREATER IN SUBJECTS WITH RISK-FACTORS CLUSTERING

Separate lines of evidence suggest that abdominal obesity, insulin, and renin are independent risk factors for coronary heart disease. Since insulin levels are higher in abdominally obese subjects and may enhance renin and aldosterone production, these risk factors may not be entirely independent. Moreover, the renin-angiotensin system may contribute to insulin resistance. These observations suggest that some inconsistencies in the literature regarding the effects of salt restriction on insulin may be explained by baseline anthropometric and metabolic differences in the subjects studied. To examine these issues, 29 volunteers with a range of risk factors were studied after 1 week each on isocaloric 20 and 200 mmol/day NaCl diets. Measurements included ambulatory blood pressures, plasma renin and aldosterone, and responses to oral glucose and intravenous insulin. Subjects were divided into three groups based on a composite score reflecting the risk factor cluster associated with abdominal obesity and hyperinsulinemia. The nine subjects with the highest scores had significantly greater values for renin and aldosterone on both the high and low salt diets than the nine subjects with the lowest scores. Pasting insulin and triglycerides, the insulin disponse to oral glucose, and plasma aldosterone all rose significantly more with salt restriction in the high than in the low risk subjects. Plasma renin activity also tended to increase more on the low salt diet in the high risk group. Ambulatory blood pressures were greater on the low than the high salt diet only in the high risk group. These data suggest that the cardiovascular risk factor cluster associated with abdominal obesity and hyperinsulinemia includes elevated renin and aldosterone levels on both high and low salt diets. The higher renin and aldosterone levels may contribute to the elevated blood pressures in subjects with risk factor clustering irrespective of salt intake. Greater activation of the renin-aldosterone axis may contribute to the rise of blood pressure and the larger increase of insulin during marked salt restriction in the high compared to low risk subjects. These findings may partially explain the variable effects of salt restriction on insulin levels in different studies.