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This Article Full Text Full Text (PDF) All Versions of this Article: 285/5/H2105    most recent 01076.2002v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via ISI Web of Science (4) Citing Articles via Google Scholar Google Scholar Articles by Cui, J. Articles by Levine, B. D. Search for Related Content PubMed PubMed Citation Articles by Cui, J. Articles by Levine, B. D.

Nitric oxide synthase inhibition does not affect regulation of muscle sympathetic nerve activity during head-up tilt

¹Institute for Exercise and Environmental Medicine, Presbyterian Hospital of Dallas, Dallas 75231; and ²Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas 75390

Submitted 13 December 2002 ; accepted in final form 30 June 2003

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 N^G-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° 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.

baroreceptors; nervous system; autonomic; orthostatic; microneurography