Sympathetic activity and the heterogenous blood pressure response to exercise training in hypertensives

To test whether changes in sympathetic nervous system (SNS) activity or insulin sensitivity contribute to the heterogeneous blood pressure response to aerobic exercise training, we used compartmental analysis of [³H]norepinephrine kinetics to determine the extravascular norepinephrine release rate (NE₂) as an index of systemic SNS activity and determined the insulin sensitivity index (S_I) by an intravenous glucose tolerance test, before and after 6 mo of aerobic exercise training, in 30 (63 ± 7 yr) hypertensive subjects. Maximal O₂ consumption increased from 18.4 ± 0.7 to 20.8 ± 0.7 ml·kg^-1·min^-1 (P = 0.02). The average mean arterial blood pressure (MABP) did not change (114 ± 2 vs. 114 ± 2 mmHg); however, there was a wide range of responses (-19 to +17 mmHg). The average NE₂ did not change significantly (2.11 ± 0.15 vs. 1.99 ± 0.13 μg·min^-1·m^-2), but there was a significant positive linear relationship between the change in NE₂ and the change in MABP (r = 0.38, P = 0.04). S_I increased from 2.81 ± 0.37 to 3.71 ± 0.42 μU × 10^-4·min^-1·ml^-1 (P = 0.004). The relationship between the change in S_I and the change in MABP was not statistically significant (r = -0.03, P = 0.89). When the changes in maximal O₂ consumption, percent body fat, NE₂, and S_I were considered as predictors of the change in MABP, only NE₂ was a significant independent predictor. Thus suppression of SNS activity may play a role in the reduction in MABP and account for a portion of the heterogeneity of the MABP response to aerobic exercise training in older hypertensive subjects.