Key result
Intravenous infusion of L-NMMA did not significantly alter the increase in muscle sympathetic nerve activity burst rate during head-up tilt compared to no L-NMMA (24 vs 23 bursts/min, P>0.05).
Why the study?
Does intravenous infusion of L-NMMA alter the regulation of muscle sympathetic nerve activity during head-up tilt in healthy subjects?
Does intravenous infusion of L-NMMA alter the regulation of muscle sympathetic nerve activity during head-up tilt in healthy subjects?
Absolute Event Rate: 24% vs 23%
p-value: p=> 0.05
Systemic inhibition of NO synthase with L-NMMA does not affect the regulation of sympathetic outflow and vascular resistance during head-up tilt in healthy humans.
L-NMMA does not alter orthostatic sympathetic regulation in healthy subjects; leaves open NO synthase role in disease states.
To test the hypothesis that systemic inhibition of nitric oxide (NO) synthase does not alter the regulation of sympathetic outflow during head-up tilt in humans, in eight healthy subjects NO synthase was blocked by intravenous infusion of NG-monomethyl-L-arginine (L-NMMA). Blood pressure, heart rate, cardiac output, total peripheral resistance (TPR), and muscle sympathetic nerve activity (MSNA) were recorded in the supine position and during 60 degrees head-up tilt. In the supine position, infusion of L-NMMA increased blood pressure, via increased TPR, and inhibited MSNA. However, the increase in MSNA evoked by head-up tilt during L-NMMA infusion (change in burst rate: 24 +/- 4 bursts/min; change in total activity: 209 +/- 36 U/min) was similar to that during head-up tilt without L-NMMA (change in burst rate: 23 +/- 4 bursts/min; change in total activity: 251 +/- 52 U/min, n = 6, all P > 0.05). Moreover, changes in TPR and heart rate during head-up tilt were virtually identical between the two conditions. These results suggest that systemic inhibition of NO synthase with L-NMMA does not affect the regulation of sympathetic outflow and vascular resistance during head-up tilt in humans.
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Cui et al. (2003) studied Healthy (n=8). NG-monomethyl-L-arginine (L-NMMA) vs. Without L-NMMA was evaluated on Change in muscle sympathetic nerve activity (MSNA) burst rate during head-up tilt (p=> 0.05). Intravenous infusion of L-NMMA did not significantly alter the increase in muscle sympathetic nerve activity burst rate during head-up tilt compared to no L-NMMA (24 vs 23 bursts/min, P>0.05).
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