SODIUM-LITHIUM COUNTERTRANSPORT IS ASSOCIATED WITH INSULIN-RESISTANCEAND URINARY ALBUMIN EXCRETION IN YOUNG AFRICAN-AMERICANS

Increased activity of the sodium transporter, sodium-lithium countertr ansport (SLC), is reported in hypertensive white patients with evidenc e of cardiac and renal injury, The purpose of this study was to determ ine whether increased SLC activity detects risk for nephropathy or vas cular disease in nondiabetic, young adult African-Americans, We examin ed 85 African-Americans aged 25 to 33 years with measurement of blood pressure, an oral glucose tolerance test to measure insulin response t o glucose challenge, and an insulin clamp for insulin sensitivity (M). Fasting plasma lipids were measured, and the V-max and K-m for Na+ we re assayed on red blood cells. Urinary albumin excretion (UAE) was mea sured on timed collections. There was a statistically significant corr elation of the V-max for SLC with M (r = -0.26, P = 0.02) and with UAE (r = 0.25, P = 0.02), The K-m for Na+ to activate SLC was also elevat ed in the subgroup of subjects with elevated V-max of SLC. There was n o significant correlation of SLC with blood pressure in bivariate anal ysis, Step-wise multiple linear regression analysis of all variables o n the V-max SLC demonstrated that plasma triglyceride, UAE, body mass index, systolic blood pressure, M, and fasting insulin were step-wise selected into the linear regression model (F-ratio = 3.2, df = 77, R = 0.46, P < 0.009). In this young adult African-American population, el evated SLC activity is detected in association with metabolic and lipi d alterations typical of insulin resistance. Elevated SLC activity is also associated with higher rates of UAE, suggesting possible evidence of early renal injury. (C) 1997 ky the National Kidney Foundation, In c.