Endothelial nitric oxide synthase mediates the nitric oxide component of reflex cutaneous vasodilatation during dynamic exercise in humans

• Published in: The Journal of physiology Vol. 592; no. 23; pp. 5317 - 5326
• Main Authors: McNamara, Tanner C., Keen, Jeremy T., Simmons, Grant H., Alexander, Lacy M., Wong, Brett J.
• Format: Journal Article
• Language: English
• Published: England Wiley Subscription Services, Inc 01.12.2014; BlackWell Publishing Ltd
• Subjects: Adult; Arginine - analogs & derivatives; Arginine - pharmacology; Body Temperature Regulation - physiology; Enzyme Inhibitors - pharmacology; Exercise - physiology; Heat Stress Disorders - physiopathology; Hemodynamics; Hot Temperature - adverse effects; Humans; Integrative; Male; Microdialysis; NG-Nitroarginine Methyl Ester - pharmacology; Nitric Oxide - physiology; Nitric Oxide Synthase Type I - antagonists & inhibitors; Nitric Oxide Synthase Type I - physiology; Nitric Oxide Synthase Type III - antagonists & inhibitors; Nitric Oxide Synthase Type III - physiology; Ornithine - analogs & derivatives; Ornithine - pharmacology; Oxygen Consumption; Reflex - physiology; Skin - blood supply; Vasodilation - drug effects; Vasodilation - physiology; Young Adult
• ISSN: 0022-3751; 1469-7793; 1469-7793
• DOI: 10.1113/jphysiol.2014.272898

Key points Increases in skin blood flow and sweating also occur during exercise; however, it is not known if the mechanisms controlling these responses are the same during passive heat stress and exercise. The prevailing thought has been that mechanisms of cutaneous vasodilatation during passive heat stress and sustained dynamic exercise are the same, or very similar. Nitric oxide (NO) has been shown to be important for increasing skin blood flow during passive heat stress but it is unknown if this molecule is also involved during sustained dynamic exercise. The findings from our study suggest NO is involved in increasing skin blood flow during sustained dynamic exercise in humans but the NO is produced from a different enzyme compared to passive heat stress. These findings may help us better understand and aid individuals who have difficulty regulating their body temperature during sustained dynamic exercise (e.g. ageing). Recent data suggests neuronal nitric oxide synthase (nNOS) mediates the NO component of reflex cutaneous vasodilatation with passive heat stress. We tested the hypothesis that nNOS inhibition would attenuate reflex cutaneous vasodilatation during sustained dynamic exercise in young healthy humans. All subjects first performed an incremental V̇O2, peak test to exhaustion on a custom‐built supine cycle ergometer. On a separate day, subjects were instrumented with four intradermal microdialysis fibres on the forearm and each randomly assigned as: (1) lactated Ringer's (control); (2) 20 mm Nω‐nitro‐l‐arginine methyl ester hydrochloride (non‐selective NOS inhibitor); (3) 5 mm N‐propyl‐l‐arginine (nNOS inhibitor); and (4) 10 mm N5‐(1‐iminoethyl)‐l‐ornithine dihydrochloride [endothelial NOS (eNOS) inhibitor]. Following microdialysis placement, subjects performed supine cycling with the experimental arm at heart level at 60% V̇O2, peak for a period sufficient to raise core temperature 0.8°C. At the end of cycling, all microdialysis sites were locally heated to 43°C and sodium nitroprusside was perfused to elicit maximal vasodilatation. Mean arterial pressure, skin blood flow via laser‐Doppler flowmetry and core temperature via ingestible telemetric pill were measured continuously; cutaneous vascular conductance (CVC) was calculated as laser‐Doppler flowmetry/mean arterial pressure and normalized to maximum. There was no significant difference between control (58 ± 2%CVCmax) and nNOS‐inhibited (56 ± 3%CVCmax) sites in response to exercise‐induced hyperthermia. The increase in CVC at eNOS‐inhibited (41 ± 3%CVCmax) and non‐selective NOS‐inhibited (40 ± 4%CVCmax) sites were significantly attenuated compared to control and nNOS‐inhibited (P < 0.001 all conditions) but there was no difference between eNOS‐inhibited and non‐selective NOS‐inhibited sites. These data suggest eNOS, not nNOS, mediate NO synthesis during reflex cutaneous vasodilatation with sustained dynamic exercise.