Evidence against elevated sympathetic vasoconstrictor activity in borderline hypertension.

The relationship between sympathetic nerve activity and BP in the early stages of essential hypertension remains unclear. To investigate this relationship further, this study measured resting muscle sympathetic nerve activity (MSNA: representing peripheral vasoconstrictor activity), plasma catecholamines, BP, central venous pressure, and heart rate in 20 young (24 +/- 2 SD yr), lean (body mass index, 24.2 +/- 3.0 kg/m2), male subjects with borderline hypertension (BHT) and in 21 male normotensive (NT) control subjects matched for age and body mass index. A cold pressor test was also performed to evaluate sympathetic reflex responsiveness. Resting mean BP and heart rate were significantly higher in the BHT subjects compared with NT subjects (113 +/- 9 versus 89 +/- 9 mmHg; 74 +/- 8 versus 62 +/- 8 bpm; P < 0.0001 each) with no difference in central venous pressure. Resting MSNA levels tended to be lower in the BHT versus the NT group (12 +/- 6 versus 14 +/- 9 bursts/min, P = NS; 16 +/- 8 versus 22 +/- 13 bursts/100 heartbeats, P = 0.05) and did not correlate with either BP or body mass index. Significant positive correlations were found between resting MSNA and plasma norepinephrine levels in both groups (P < 0.05). Hemodynamic and sympathetic nerve responses to the cold pressor test were similar between the BHT and NT subjects. It is concluded that resting MSNA and plasma norepinephrine levels are correlated in young lean NT and BHT men; however, neither of these variables is correlated with BP. Because MSNA was similar in the two groups, the concept that augmented resting MSNA is important in the early developmental phase of essential hypertension must be reevaluated.