title: Influence of α-adrenergic vasoconstriction on the blunted skeletal muscle contraction-induced rapid vasodilation with aging.
abstract: We tested the hypothesis that elevated sympathetic tone is responsible for lower peak vasodilation after single muscle contractions in older adults. Young (n = 13, 7 men and 6 women, age: 27 ± 1 yr) and older (n = 13, 7 men and 6 women, age: 69 ± 2 yr) adults performed single forearm contractions at 10%, 20%, and 40% of maximum during 1) control, 2) sympathetic activation via lower body negative pressure (LBNP; -20 mmHg), and 3) intra-arterial infusion of phentolamine (α-adrenergic antagonist). Brachial artery diameter and velocities were measured via Doppler ultrasound, and forearm vascular conductance (FVC; in ml·min(-1)·100 mmHg(-1)) was calculated from blood flow (in ml/min) and blood pressure (in mmHg). Peak vasodilator responses [change in (Δ) FVC from baseline] were attenuated in older adults at 20% and 40% of maximum (P < 0.05). LBNP reduced peak ΔFVC at 10% (98 ± 17 vs. 70 ± 12 ml·min(-1)·100 mmHg(-1)), 20% (144 ± 12 vs. 98 ± 3 ml·min(-1)·100 mmHg(-1)), and 40% (209 ± 20 vs. 161 ± 21 ml·min(-1)·100 mmHg(-1), P < 0.01 vs. control) in younger adults but not in older adults (71 ± 11 vs. 68 ± 11, 107 ± 13 vs. 106 ± 16, and 161 ± 22 vs. 144 ± 22 ml·min(-1)·100 mmHg(-1), respectively, P = 0.22-0.99). With phentolamine, peak ΔFVC was enhanced in older adults at each contraction intensity (100 ± 14, 147 ± 22, and 200 ± 26 ml·min(-1)·100 mmHg(-1), respectively, P < 0.01 vs. control) but not in younger adults (94 ± 13, 153 ± 13, and 224 ± 27 ml·min(-1)·100 mmHg(-1), respectively, P = 0.30-0.81 vs. control). Our data indicate that α-adrenergic vasoconstriction and/or blunted functional sympatholysis might contribute to the age-related decreases in skeletal muscle contraction-induced rapid vasodilation in humans.
authors.affiliation: Department of Anesthesiology, Mayo Clinic, 200 First Street SW, Rochester, MN 55905, USA. casey.darren@mayo.edu
authors.forename: Darren P
authors.initials: DP
authors.lastname: Casey
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Joyner
mesh_terms: D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology*; D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology*; 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 / Q000502:physiology; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology; D006439:Hemodynamics / Q000187:drug effects / Q000502:physiology; D006801:Humans; D007261:Infusions, Intra-Arterial / Q000379:methods; D008150:Lower Body Negative Pressure / Q000379:methods; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology*; D018482:Muscle, Skeletal / Q000098:blood supply / Q000187:drug effects / Q000502:physiology*; D010646:Phentolamine / Q000494:pharmacology; D012039:Regional Blood Flow / Q000187:drug effects / Q000502:physiology; D013564:Sympathetic Nervous System / Q000187:drug effects / Q000502:physiology; D014661:Vasoconstriction / Q000187:drug effects / Q000502:physiology*; D014664:Vasodilation / Q000187:drug effects / Q000502:physiology*
chemical_list: D000317:Adrenergic alpha-Antagonists; D010646:Phentolamine