title: Nitric oxide synthase inhibition does not affect regulation of muscle sympathetic nerve activity during head-up tilt.
abstract: 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.
authors.affiliation: Institute for Exercise and Environmental Medicine, Presbyterian Hospital of Dallas, 7232 Greenville Avenue, Dallas, TX 75231, USA.
authors.forename: Jian
authors.initials: J
authors.lastname: Cui
authors.forename: Rong
authors.initials: R
authors.lastname: Zhang
authors.forename: Thad E
authors.initials: TE
authors.lastname: Wilson
authors.forename: Sarah
authors.initials: S
authors.lastname: Witkowski
authors.forename: Craig G
authors.initials: CG
authors.lastname: Crandall
authors.forename: Benjamin D
authors.initials: BD
authors.lastname: Levine
mesh_terms: D000328:Adult; D001794:Blood Pressure / Q000187:drug effects / Q000502:physiology; D002302:Cardiac Output / Q000187:drug effects / Q000502:physiology; D004791:Enzyme Inhibitors / Q000008:administration & dosage*; D005260:Female; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal / Q000294:innervation; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors*; D011311:Pressoreceptors / Q000187:drug effects / Q000502:physiology; D016683:Supine Position / Q000502:physiology; D013564:Sympathetic Nervous System / Q000187:drug effects* / Q000502:physiology; D018667:Tilt-Table Test; D014655:Vascular Resistance / Q000187:drug effects / Q000502:physiology; D019323:omega-N-Methylarginine / Q000008:administration & dosage*
chemical_list: D004791:Enzyme Inhibitors; D019323:omega-N-Methylarginine; D019001:Nitric Oxide Synthase