Epidemiologic studies have demonstrated a greater prevalence of essential hypertension (EH) in blacks with a disproportionately greater hypertension related mortality in blacks. Similar vascular consequences occur with diabetes and obesity. These three diseases not only share a common outcome, but also overlap in occurrence with blacks having greater prevalence rates in the three disorders. Insulin resistance has been documented in all three disorders (EH, diabetes, obesity) and may contribute significantly to the vascular disease. In a preceding study, we have demonstrated a greater prevalence of sodium sensitivity in young adult blacks than whites. Stress induced cardiovascular reactivity proved to be greater in whites than blacks. In both races, reactivity was greater in those with a family history of EH. Sodium loading, however, did not augment the stress induced reactivity. Therefore, the pressor effect imposed by sodium loading was a peripheral increase in vascular resistance and not a cardiac increase in flow. Variations in cation cotransport correlated with sodium sensitivity. The objective of this proposed three year project is to investigate the role of insulin resistance in relation to peripheral vascular hemodynamics, sodium sensitivity and blood pressure regulation in a representative young adult (22-26 years) black population (RBS) and a group of young blacks at high risk for EH (borderline hypertension). The subjects in this project consist of blacks who were enrolled in the Collaborative Perinatal Project (CPP) at birth. These subjects have been studied longitudinally in adolescence (HL 19869), young adulthood (HL 26898), and in a preceding project on biobehavioral factors affecting EH in young blacks (HL 31802). We will study peripheral vascular structure using measures of forearm blood flow and forearm vascular resistance. We will study insulin resistance using the euglycemic hyperinsulinemic clamp technique. We will study further cation transport mechanisms, in particular Na-Proton exchange. Peripheral vascular resistance and insulin sensitivity/resistance will be interrelated with sodium sensitivity and potassium sensitivity in the normotensive (RBS) and borderline hypertensive (RBH) blacks. The overall hypothesis is: Insulin resistance will correlate with sodium sensitivity and greater peripheral vascular resistance in blacks at high risk for EH.
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