title: Contribution of nitric oxide in the contraction-induced rapid vasodilation in young and older adults.
abstract: We tested the hypothesis that reduced nitric oxide (NO) bioavailability contributes to the attenuated peak and total vasodilation following single-muscle contractions in older adults. Young (n = 10; 24 ± 2 yr) and older (n = 10; 67 ± 2 yr) adults performed single forearm contractions at 10, 20, and 40% of maximum during saline infusion (control) and NO synthase (NOS) inhibition via N(G)-monomethyl-l-arginine. Brachial artery diameters and velocities were measured using Doppler ultrasound and forearm vascular conductance (FVC; in ml·min(-1)·100 mmHg(-1)) was calculated from blood flow (ml/min) and blood pressure (mmHg). Peak and total vasodilator responses [change (Δ) in FVC from baseline] were attenuated in older adults at all intensities (P < 0.05). NOS inhibition reduced the peak ΔFVC at 10% (88 ± 12 vs. 52 ± 9 ml·min(-1)·100 mmHg(-1)), 20% (125 ± 13 vs. 83 ± 13 ml·min(-1)·100 mmHg(-1)), and 40% (207 ± 26 vs. 133 ± 20 ml·min(-1)·100 mmHg(-1)) in young subjects, (P < 0.05 for all) and in older adults at 10% (59 ± 5 vs. 47 ± 7 ml·min(-1)·100 mmHg(-1), P < 0.05) and 20% (88 ± 9 vs. 68 ± 9 ml·min(-1)·100 mmHg(-1), P < 0.05), but not 40% (128 ± 12 vs. 105 ± 11 ml·min(-1)·100 mmHg(-1), P = 0.11). The relative (%) reduction in peak ΔFVC due to NOS inhibition was greater in young vs. older adults at 20% (-36 ± 5 vs. -23 ± 5%, P < 0.05) and 40% (-35 ± 6 vs. -16 ± 7%, P < 0.05). The reduction in the total vasodilator response (area under the curve) with NOS inhibition was also greater in young vs. older adults at all intensities. Our data suggest that contraction-induced rapid vasodilation is mediated in part by NO, and that the contribution of NO is greater in young adults.
authors.affiliation: Department of Physical Therapy and Rehabilitation Science, Carver College of Medicine, University of Iowa, Iowa City, Iowa 52242, USA. darren-casey@uiowa.edu
authors.forename: Darren P
authors.initials: DP
authors.lastname: Casey
authors.forename: Branton G
authors.initials: BG
authors.lastname: Walker
authors.forename: Sushant M
authors.initials: SM
authors.lastname: Ranadive
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Taylor
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Joyner
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000328:Adult; D000367:Age Factors; D000368:Aged; D001783:Blood Flow Velocity / Q000187:drug effects / Q000502:physiology; D001794:Blood Pressure / Q000187:drug effects / Q000502:physiology; D001916:Brachial Artery / Q000187:drug effects / Q000502:physiology; D005260:Female; D005542:Forearm / Q000098:blood supply; D006439:Hemodynamics / Q000187:drug effects / Q000502:physiology; D006801:Humans; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology*; D018482:Muscle, Skeletal / Q000098:blood supply / Q000187:drug effects / Q000502:physiology; D009569:Nitric Oxide / Q000493:pharmacokinetics / Q000494:pharmacology*; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors / Q000378:metabolism; D009599:Nitroprusside / Q000494:pharmacology; D012039:Regional Blood Flow / Q000187:drug effects / Q000502:physiology; D014664:Vasodilation / Q000187:drug effects* / Q000502:physiology; D014665:Vasodilator Agents / Q000494:pharmacology*; D055815:Young Adult
chemical_list: D014665:Vasodilator Agents; D009599:Nitroprusside; D009569:Nitric Oxide; D019001:Nitric Oxide Synthase; D000109:Acetylcholine
keywords: aging; muscle contraction; nitric oxide; vasodilation