Influence of angiotensin II blockade during exercise in the heat.

The effect of the blockade of the renin angiotensin system (RAS) on thermoregulatory, cardiovascular and renal function during moderate exercise in a hot [mean (SEM) 34.4 (0.1) degrees C] environment was evaluated. Six men and three women cycled at 60% peak oxygen uptake for 45 min following acute administration of a placebo (PLAC) or enalapril (ENAL), an angiotensin converting enzyme inhibitor (ACE-I). Resting mean arterial pressure (MAP) was reduced by ENAL, but the pressor response to exercise was unaffected [delta MAP = 7.8 (1.4)mmHg for both trials (P > 0.05)]. Peak esophageal temperature [T(es) = 38.7 (1.0) degrees C (PLAC) vs 38.4 (0.2) degrees C (ENAL)] and mean skin temperatures [Tsk = 36.5 (0.1) degrees C (PLAC) vs 36.6 (0.1) degrees C (ENAL)] were similar for both drug treatments during the exercise. Both aldosterone and plasma renin activity (PRA) increased five fold above resting values during exercise; however, only the PRA response [16.7 (3.2) ng angiotensin I (Ang I).ml-1.h-1 (ENAL) vs 7.4 (1.2)ng Ang I.ml-1.h-1 (PLAC)] was significantly altered by ENAL treatment (P < 0.05). Urine flow, sodium excretion and glomerular filtration rates, determined from creatinine clearance, were similarly reduced following exercise for both ENAL and PLAC treatments. These results suggest acute administration (5 mg) of ACE-I does not impair thermoregulatory, cardiovascular or renal responses during moderate exercise in the heat.