Urinary acid-base excretion in normotensives and hypertensives of African origin

Abnormalities in acid-base regulation have previously been reported both in hypertensive humans and animals and a link between abnormalities in renal sodium handling and acid excretion may be particularly important in black h ypertensives. The objectives of this study were to compare indices of urina ry acid excretion (urinary pH, ammonium and titratable acid excretion) betw een normotensives and hypertensive people of African origin. Measurements w ere carried out in 86 black individuals of African origin in a case-control design (19 normotensive; 67 hypertensive). Of these, 17 normotensive and 1 7 patients with essential hypertension were matched for age, sex and weight . Group comparisons were carried out by unpaired t-tests or two-way analysi s of variance and group values are given as means +/- s.d. Urinary pH was s ignificantly higher in the hypertensives both in the unmatched groups and i n the matched groups. In the 17 matched pairs: urinary pH in the hypertensi ve individuals was 6.36+/-0.54 and 5.84 a 0.53 in the normotensives, respec tively; P= 0.007. Additionally, urinary titratable acidity was significantl y lower in the hypertensives than in the normotensives (25.4 +/- 13.7 vs 16 .7 +/- 10.7 mmol/24 h; P= 0.047) but there were no significant differences in urinary ammonium excretion. The mechanisms for the apparent reduction in acid excretion in the hypertensives is not clear but these results highlig ht the possibility that hypertension in blacks is associated with abnormali ties of renal sodium and hydrogen exchange with compensatory increases in r enal ammonium production.