title: The contribution of nitric oxide to exercise hyperemia in the human forearm.
abstract: The contribution of nitric oxide (NO) to exercise-induced hyperemia is debated. Previous conclusions that nitric oxide synthase (NOS) inhibition reduces endothelium-dependent vasodilation during exercise hyperemia may be confounded by inhibitor-mediated increases in resting vascular tone. In this study, nine healthy participants performed wrist flexion exercise before and during intra-arterial administration of the NOS-inhibitor NG-monomethyl-L-arginine (L-NMMA, 2 mg x min(-1)). Nine additional subjects performed this procedure while nitroprusside (0.2 microg x min(-1)) was co-infused with L-NMMA to maintain basal flow. Forearm blood flow was assessed with venous occlusion strain-gauge plethysmography at baseline, immediately after cessation of exercise, and continuously for 5 minutes thereafter. L-NMMA alone reduced resting flow by 26%, peak flow immediately after exercise by 20%, and integrated post-exercise hyperemic volume by 50% (all p < 0.05). Stabilization of resting vasodilator tone by nitroprusside eliminated the effects of L-NMMA on peak flow after exercise, yet L-NMMA still attenuated total hyperemic volume. In a time-control study of 12 subjects, there was no change in peak blood flow or hyperemic volume. This study indicates that NO is not a major regulator of peak limb blood flow measured immediately after cessation of dynamic exercise. The contribution of NO to exercise hyperemia is limited to the recovery period after exercise.
authors.affiliation: Harvard Medical School '03, Boston, MA, USA.
authors.forename: Mary Beth
authors.initials: MB
authors.lastname: Gordon
authors.forename: Rajiv
authors.initials: R
authors.lastname: Jain
authors.forename: Joshua A
authors.initials: JA
authors.lastname: Beckman
authors.forename: Mark A
authors.initials: MA
authors.lastname: Creager
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000293:Adolescent; D000328:Adult; D001794:Blood Pressure / Q000187:drug effects / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015444:Exercise / Q000502:physiology*; D005260:Female; D005542:Forearm / Q000098:blood supply*; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology; D006801:Humans; D006940:Hyperemia / Q000503:physiopathology*; D007261:Infusions, Intra-Arterial; D008297:Male; D009569:Nitric Oxide / Q000502:physiology*; D019001:Nitric Oxide Synthase / Q000187:drug effects / Q000502:physiology; D009599:Nitroprusside / Q000494:pharmacology; D012016:Reference Values; D012039:Regional Blood Flow / Q000187:drug effects / Q000502:physiology; D015203:Reproducibility of Results; D014655:Vascular Resistance / Q000187:drug effects / Q000502:physiology; D014664:Vasodilation / Q000187:drug effects / Q000502:physiology; D014665:Vasodilator Agents / Q000494:pharmacology; D019323:omega-N-Methylarginine / Q000494:pharmacology
chemical_list: D004791:Enzyme Inhibitors; D014665:Vasodilator Agents; D009599:Nitroprusside; D019323:omega-N-Methylarginine; D009569:Nitric Oxide; D019001:Nitric Oxide Synthase; D000109:Acetylcholine