Racial differences in resting end-tidal CO2 and circulating sodium pump inhibitor

Previous studies have shown that high end-tidal CO, (PetCO(2)) is a marker for sodium sensitivity of blood pressure (BP) in White Americans, and that the BP of African Americans is more sensitive to high sodium intake than th at of whites. The present study tested the hypothesis that resting PetCO(2) is higher in normotensive African Americans than in whites. Resting end-ti dal CO2 of 395 white and 125 African American participants in the Baltimore Longitudinal Study on Aging was monitored for 20 min with a respiratory ga s monitor, and BP and heart rate were recorded every 5 min by oscillometric methodology. Twenty-four-hour urinary excretion of a circulating sodium pu mp inhibitor marinobufagenin-like compound (MBG), which increases when plas ma volume is expanded, was also analyzed by fluoroimmunoassay in racial gro ups. Mean resting PetCO(2) of African American men was higher than that of white men (38.1 +/- 0.5 v 36.4 +/- 0.3 mm Hg), and resting PetCO(2) of Afri can American women was higher than that of white women (37.7 +/- 0.3 v 36.2 +/- 0.3 rum Hg). The differences were not significant in either men or wom en less than 50 years old, but were substantial in both men and women more than 50 years. Twenty-four-hour urinary excretion of MBG was higher in whit e (2.7 +/- 0.2 pmol) than in African American (2.1 +/- 0.2 pmol) participan ts, and high PetCO(2) was a significant independent predictor of high MBG e xcretion in African Americans, These data are consistent with the hypothesi s that the higher resting PetCO(2) in African Americans plays a role in slo wer urinary excretion of sodium, greater BP sensitivity to high sodium inta ke, and increased prevalence of chronic hypertension. (C) 2001 American Jou rnal of Hypertension. Ltd.