Racial differences in potassium disposal

Background. African Americans appear relatively potassium (K ⁺)-deficient compared with Caucasian Americans whether on unregulated diets or on diets controlled for K⁺ content. Methods. To determine whether extrarenal K⁺ disposal was affected by race, KCl (0.5 mEq/kg in 0.9% saline) was infused over 48 minutes to 12 African American and 12 Caucasian American normotensive, healthy subjects. Identical infusions were administered before and after 10 days of fixed electrolyte intake. In addition to serum K⁺, glucose, insulin, renin, and aldosterone were measured in blood, and K⁺ and sodium (Na⁺) in urine voided spontaneously during the infusions. Data were analyzed using a two-factor analysis of variance (ANOVA) with repeated measures. Results. Basal serum K ⁺ did not differ between races (African American 3.97 ± 0.06 mEq/L and Caucasian American 3.98 ± 0.05, P = NS). The rise in serum K⁺ during the infusion and the area under the curve of serum K ⁺ over the 3.5 hours of observation were both greater in African American (African American +0.82 ± 0.07 mEq/L and Caucasian American +0.61 ± 0.06, P = 0.001; and African American 6.9 ± 0.5 units and Caucasian American 5.1 ± 0.6, F = 0.0012). The 10-day period of controlled intake did not abolish these differences. Aldosterone at baseline was lower and insulin was higher in African Americans at the end of the infusion. Urinary K⁺, plasma glucose, and renin levels did not differ between African Americans and Caucasian Americans. Conclusion. Disposal of an intravenous (iv) K⁺ load is decreased in African Americans compared with Caucasian Americans, which may reflect decreased Na⁺,K ⁺-ATPase activity in African Americans in vivo.