In-vivo intracellular pH at rest and during exercise in patients with essential hypertension

Background Several studies in isolated cells have reported that intracellul ar pH (pHi) in individuals with essential hypertension may be relatively al kaline compared to normotensive individuals. Such an abnormality of pHi in hypertension would be consistent with enhanced sodium-hydrogen exchanger ac tivity and may provide potential mechanisms by which hypertension and its c omplications could develop. Objectives To determine in-vivo intracellular pH of skeletal muscle at rest and during recovery from exercise-induced acidosis in hypertensive and nor motensive subjects. Methods Using 31-phosphorus magnetic resonance spectroscopy, pHi of the dom inant flexor digitorum superficialis was measured in 20 Caucasian subjects (14 male) with essential hypertension and 20 normotensive controls matched for gender, age, race and body mass index. Measurements were made at rest a nd during the exercise and recovery periods of a stepped incremental maxima l exercise protocol. The rate of pHi recovery from exercise-induced acidosi s was calculated by linear regression over the first 210 s of recovery from the pHi time plots of respective subjects. Results Mean resting pHi in the hypertensive (7.05 +/- 0.04) and normotensi ve groups (7.06 +/- 0.04) were not significantly different There was a sign ificant effect of gender on pHi: mean pHi was 7.07 +/- 0.03 in males and 7. 02 +/- 0.03 in females, respectively (P < 0.0005). The mean intracellular p H achieved by exercise was 6.74 +/- 0.31 in hypertensive individuals and no t significantly different in normotensive individuals (6.68 +/- 0.19; P = 0 .4). The mean rate of pHi recovery in the hypertensives was 0.08 +/- 0.03 p H units/min and not significantly different in normotensives (0.08 +/- 0.02 ; P = 0.4). Conclusions These results contrast with previously documented abnormalities in the control of pHi in hypertension and demonstrate the absence of major in-vivo disturbances of pHi in skeletal muscle, both at rest and during re covery from exercise-induced acidosis, in essential hypertension. Therefore , it is possible that previously documented abnormalities of pHi and activi ty of the exchanger may be either specific to cell type or not present unde r in-vivo conditions. (C) 2001 Lippincott Williams & Wilkins.