Sodium-lithium countertransport is associated with insulin resistance and urinary albumin excretion in young African-Americans.

Increased activity of the sodium transporter, sodium-lithium countertransport (SLC), is reported in hypertensive white patients with evidence of cardiac and renal injury. The purpose of this study was to determine whether increased SLC activity detects risk for nephropathy or vascular disease in nondiabetic, young adult African-Americans. We examined 85 African-Americans aged 25 to 33 years with measurement of blood pressure, an oral glucose tolerance test to measure insulin response to glucose challenge, and an insulin clamp for insulin sensitivity (M). Fasting plasma lipids were measured, and the Vmax and Km for Na+ were assayed on red blood cells. Urinary albumin excretion (UAE) was measured on timed collections. There was a statistically significant correlation of the Vmax for SLC with M (r = -0.26, P = 0.02) and with UAE (r = 0.25, P = 0.02). The Km for Na+ to activate SLC was also elevated in the subgroup of subjects with elevated Vmax of SLC. There was no significant correlation of SLC with blood pressure in bivariate analysis. Step-wise multiple linear regression analysis of all variables on the Vmax 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, elevated SLC activity is detected in association with metabolic and lipid alterations typical of insulin resistance. Elevated SLC activity is also associated with higher rates of UAE, suggesting possible evidence of early renal injury.