Aging is associated with a decline in physical activity and an increase in body fat, which leads to the development of insulin resistance and hyperinsulinemia. These metabolic changes may raise BP in the elderly by increasing sensitivity to dietary sodium and causing sodium and water retention to reduce renal plasma flow (RPF) and increase glomerular filtration rate (GFR) to raise intrarenal pressure. The hypothesis is that the decrease in physical activity and increase in visceral body fat with aging increases insulin resistance and hyperinsulinemia to increase filtration fraction and peritubular sodium resorption thereby raising blood volume and sympathetic nervous system activity (SNS) to elevate BP. Thus. interventions which increase physical activity and decrease total body fat will enhance natriuresis and lower BP by increasing insulin sensitivity and improving renal hemodynamics. The mechanisms by which nutritional (sodium restriction and WL) and AEX interventions lower BP in older hypertensives will be examined in black and white patients aged 55- 75 yrs. The effects of dietary sodium on renal hemodynamics (measurement of RPF (1311-Hippuran) and GFR (99T-DTPA)] and BP, SNS and insulin sensitivity (multi-dose hyperinsulinemic euglycemic clamp) will be examined by random assignment of patients to a high (10 g/day) and than a low (3 g/day) sodium diet or vice versa for 2-weeks at baseline and after 6 mo AEX+WL intervention. An improved understanding of the relation between dietary sodium and insulin resistance may assist us in devising nonpharmacological measures (dietary sodium restrict, AEX, WL) in the prevention and treatment of HTN in the elderly.
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