title: Nitric oxide is not obligatory for radial artery flow-mediated dilation following release of 5 or 10 min distal occlusion.
abstract: This study investigated the nitric oxide (NO) dependence of radial artery (RA) flow-mediated dilation (FMD) in response to three different reactive hyperemia (RH) shear stimulus profiles. Ten healthy males underwent the following three RH trials: 1) 5 min occlusion (5 trial), 2) 10 min occlusion (10 trial), and 3) 10 min occlusion with cuff reinflation at 30 s (10-30 trial). Trials were performed during saline infusion and repeated during N(G)-monomethyl-L-arginine (L-NMMA) infusion in the brachial artery. RA blood flow velocity was measured with Doppler ultrasound, and B-mode RA images were analyzed using automated edge detection software. Shear rate estimation of shear stress was calculated as the blood flow velocity/vessel diameter. L-NMMA decreased baseline vascular conductance by 35%. L-NMMA infusion did not affect the peak shear rate stimulus (P = 0.681) or the area under the curve (AUC) of shear rate to peak FMD (P = 0.088). The AUC was significantly larger in the 10 trial vs. the 10-30 or 5 trial (P < 0.001). Although percent FMD (%change in diameter) in the 10 trial was larger than that in the 5 trial (P = 0.035), there was no significant difference in %FMD between the saline and L-NMMA conditions in any trial: 5 trial, 5.62 +/- 1.48 vs. 5.63 +/- 1.27%; 10 trial, 9.07 +/- 1.16 vs. 11.22 +/- 2.21%; 10-30 trial, 6.52 +/- 1.43 vs. 7.98 +/- 1.51% for saline and L-NMMA, respectively (P = 0.158). We conclude the following: 1) RH following 10 min of occlusion results in an enhanced stimulus and %FMD compared with 5 min of occlusion. 2) When the occlusion cuff is reinflated 30 s postrelease of a 10 min occlusion, it does not result in an enhanced %FMD compared with that which results from RH following 5 min of occlusion. 3) The lack of effect of L-NMMA on FMD suggests that NO may not be obligatory for radial artery FMD in response to either 5 or 10 min of occlusion in healthy volunteers.
authors.affiliation: School of Kinesiology and Health Studies, Queen's University, Kingston, Ontario, Canada.
authors.forename: Kyra
authors.initials: K
authors.lastname: Pyke
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Green
authors.forename: Cara
authors.initials: C
authors.lastname: Weisbrod
authors.forename: Matthew
authors.initials: M
authors.lastname: Best
authors.forename: Lawrence
authors.initials: L
authors.lastname: Dembo
authors.forename: Gerry
authors.initials: G
authors.lastname: O'Driscoll
authors.forename: Michael
authors.initials: M
authors.lastname: Tschakovsky
mesh_terms: D000328:Adult; D019540:Area Under Curve; D001157:Arterial Occlusive Diseases / Q000503:physiopathology*; D001794:Blood Pressure / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D006940:Hyperemia / Q000503:physiopathology; D008297:Male; D009569:Nitric Oxide / Q000502:physiology*; D052250:Nitric Oxide Synthase Type III / Q000037:antagonists & inhibitors; D017534:Radial Artery / Q000502:physiology*; D012039:Regional Blood Flow / Q000502:physiology; D013314:Stress, Mechanical; D014664:Vasodilation / Q000502:physiology*; D055815:Young Adult; D019323:omega-N-Methylarginine / Q000494:pharmacology
chemical_list: D004791:Enzyme Inhibitors; D019323:omega-N-Methylarginine; D009569:Nitric Oxide; D052250:Nitric Oxide Synthase Type III