Race and physical activity: cardiovascular and renal response to sodium loading

Race and level of physical activity may be important factors affecting cardiovascular responsiveness to acute sodium intake. We examined the effects of a 4-day sodium loading procedure on heart rate (HR), systolic (SBP) and diastolic (DBP) blood pressure, 24-hour electrolyte excretion, and extracellular fluid volume (ECF) in African-American (n = 16) and Caucasian (n = 16) adult males. All subjects were normotensive with either moderately high (> or = 3 day/wk; > or = 20 min/day) or low (< or = 3 day/wk; < or = 20 min/day) physical activity levels. Subjects ingested either placebo or NaCl (0.2 g/kg/day) during two 4-day periods. Sodium loading increased SBP and decreased HR in all high physical activity subjects but not in low physical activity subjects (p < 0.05). Na+ excretion did not differ among groups, although urine volume and K+ excretion were lower, and Na+/K+ excretion ratio was higher in African-American compared to Caucasian subjects (p < 0.05). ECF, as measured by NaBr dilution, was greater in high physical activity subjects compared to low physical activity subjects (p < 0.05). These data suggest that high physical activity levels do not attenuate but rather exaggerate SBP response to a sodium load.