Albuminuria in Association With Insulin and Sodium-Lithium Countertransport in Young African Americans With Borderline Hypertension

Abstract

Abstract The purpose of this study was to determine whether early nephropathy, evidenced by urinary albumin excretion, can be detected in young African American subjects with only borderline hypertension, and whether there is a relationship of albuminuria with insulin resistance and with sodium-lithium countertransport activity. Clinically well young African American men and women including normotensive (blood pressure <135/85 mm Hg, n=41) and borderline hypertensive (blood pressure ≥135/85 mm Hg, n=26) individuals were studied. Each subject underwent an oral glucose tolerance test and euglycemic hyperinsulinemic clamp study. Albuminuria was measured on timed urine collections. Sodium-lithium countertransport activity was assayed in fresh red blood cells at 280 mmol/L Na + for full saturation of external Na + sites. The sum of insulin levels during glucose tolerance was significantly greater in the borderline hypertensive compared with the normotensive subjects ( P =.014), and insulin-stimulated glucose utilization during the clamp was significantly lower in borderline hypertensive compared with normotensive subjects ( P =.016). Albuminuria was greater in borderline hypertensive compared with normotensive subjects ( P =.002). Albuminuria was significantly correlated with fasting plasma insulin concentration ( r =.44, P <.002) and the sum of insulins during the glucose tolerance test ( r =.45, P <.002). Sodium-lithium countertransport correlated with albuminuria ( r =.31, P <.05) as well as significantly with insulin-stimulated glucose utilization during the clamp ( r =.44, P <.001). These data indicate that young African Americans with only borderline hypertension have greater albuminuria than normotensive subjects and suggest that albuminuria is linked with insulin resistance and alterations of sodium-lithium countertransport that may increase the risk for nephropathy.