Contribution of nitric oxide to exercise-induced hypotension in human sympathetic denervation

The cardiovascular, catecholamine, and nitrate/nitrite (NO) responses to bicycle exercise were measured in 14 normal subjects (controls) and two groups with sympathetic denervation; 14 with peripheral autonomic failure (pure autonomic failure [PAF]); and 13 with central autonomic failure (multiple system atrophy [MSA]). With exercise, blood pressure increased in control subjects by 40 +/- 7/24 +/- 5 mm Hg (p < 0.001) and fell in PAF by 24 +/- 8/24 +/- 5 mm Hg (p < 0.02 and p < 0.007) and MSA by 31 +/- 7/11 +/- 3 mm Hg (p < 0.005 and p < 0.04). With exercise, the increase in heart rate was greater in control subjects (60 +/- 3 to 111 +/- 4/min; p < 0.0001) than in PAF (69 +/- 3 to 86 +/- 4/min; p < 0.0001) and MSA (70 +/- 4 to 90 +/- 4; p < 0.001). Resting plasma noradrenaline levels were similar in controls (291 +/- 51 pg ml(-1)) and MSA (257 +/- 49 pg ml(-1)), but lower in PAF (82 +/- 14 pg ml(-1)). With exercise, plasma noradrenaline increased in controls but was unchanged in PAF and MSA. Resting NOx was similar in controls (50 +/- 5 nmol/L; range, 23.3-87.6 nmol/L) and PAF patients (59+/-8 nmol/l; range, 19.3-116.4 nmol/L), but was higher in MSA patients (87 +/-14 nmol/L; p <0.025, range 15.4-157.2 nmol/L). With exercise, NOx was unchanged in control subjects and increased by 10% and 17% in PAF and MSA, respectively; these changes were not statistically significant. This study suggests that circulating changes in NOx levels do not exert a major role in exercise-induced hypotension in subjects with sympathetic denervation.