Effect of acute administration of vitamin C on muscle sympathetic activity, cardiac sympathovagal balance, and baroreflex sensitivity in hypertensive patients

Background: Essential hypertension is characterized by both increased oxidative stress and sympathetic traffic. Experimental studies have shown that reactive oxygen species can modulate autonomic activity. Objective: The aim of this study was to determine whether acute administration of the antioxidant vitamin C modifies sympathetic nerve activity in essential hypertension. Design: Thirty-two untreated patients with essential hypertension and 20 normotensive subjects received vitamin C (3 g intravenously in 5 min) or vehicle. Heart rate, noninvasive beat-to-beat blood pressure, and muscle sympathetic nerve activity (microneurogra- phy) were monitored at baseline and up to 20 min after the infusion. Spectral analysis of RR interval variability and spontaneous barore- flex sensitivity were also computed. Results: Vitamin C infusion significantly lowered blood pressure in hypertensive patients but not in normotensive subjects (maximal changes in systolic blood pressure: 24.9 6 10.1 compared with 20.7 6 4.0 mm Hg, respectively; P , 0.05). Moreover, muscle sympathetic nerve activity was significantly reduced after vitamin C infusion in hypertensive patients (from 53.3 6 12.2 to 47.4 6 11.5 bursts/100 heart beats; P , 0.01) but not in healthy subjects (from 42.0 6 10.1 to 42.7 6 11.8 bursts/100 heart beats; NS). On the contrary, in 16 hypertensive patients, sodium nitroprusside in equi- depressor doses induced a significant increase in muscle sympathetic nerve activity compared with vitamin C (+10.0 6 6.9 bursts/100 heart beats). Sympathovagal balance and spontaneous baroreflex sensitiv- ity were restored during vitamin C infusion in hypertensive subjects. Conclusions: These results indicate that acute administration of vita- min C is able to reduce cardiovascular adrenergic drive in hyperten- sive patients, which suggests that oxidative stress is involved in the regulation of sympathetic activity in essential hypertension.