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Sympathetic Nervous System Activation Reduces Contraction‐induced Rapid Vasodilation in the Leg of Humans Independent of Age
Author(s) -
Hughes William E,
Kruse Nicholas T,
Casey Darren P
Publication year - 2017
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.31.1_supplement.840.24
Subject(s) - vasodilation , medicine , forearm , cardiology , contraction (grammar) , ageing , skeletal muscle , heart rate , sympathetic nervous system , blood pressure , muscle contraction , blood flow , endocrinology , anatomy
Aging is associated with attenuated vasodilation and hyperemia following a single skeletal muscle contraction in both the arm and leg. We previously demonstrated that enhanced sympathetic vasoconstrictor tone contributes to the blunted skeletal muscle contraction‐induced rapid onset vasodilation (ROV) in the forearm of older adults. However, evidence suggests that limb‐specific differences in the regulation of vascular tone exist with aging. Therefore, we sought to examine whether elevated sympathetic tone in the leg contributes to the age‐related reductions in contraction‐induced ROV. Healthy, young (n=13; 24±1yr; 7M/6F) and older (n=10; 67±1yr; 6M/4F) adults performed single muscle contractions in the right leg [20% and 40% work rate maximum (WR max )] under control (no sympathetic stimulus) and enhanced sympathetic nervous system activity (via a cold pressor test; CPT) conditions. CPT testing consisted of placing the left foot in an ice‐water bath (4° C) for 4 minutes. Femoral artery diameter and mean blood velocity were measured using Doppler ultrasound. Leg vascular conductance (VC; ml· min −1 · 100mmHg −1 ) was calculated using blood flow (mL· min −1 ) and mean arterial pressure (mmHg). Under control conditions, peak (ΔVC from baseline) and total (area under the curve over 30 cardiac cycles post contraction) vasodilator responses were attenuated in older adults across exercise intensities (P<0.05). Increased sympathetic vasoconstrictor tone via CPT reduced peak and total VC responses in both young and older adults across exercise intensities (P<0.05). The magnitude (%) of reduction did not differ between young vs. older adults for peak (20% WR max : −25±5% vs. −22±4%, P=0.57 and 40% WR max : −21±6% vs. −29±6%, P=0.37) or total VC (20% WR max : −28±5% vs. −37±7%, P=0.29 and 40% WR max : −22±8% vs. −35±7%, P=0.20). Due to differences in WR max between age groups, comparisons in the ROV response were also made in a subset of subjects (9 young/8 older) matched for an approximate absolute workload (~10W). Workload matched responses revealed that age‐associated reductions in peak ΔVC and total VC under control conditions still persisted (P<0.05). Moreover, there were no differences in the magnitude of reduction in peak (−20±7% vs. −24±5%, P=0.34) or total VC (−22±8% vs. −29±4%, P=0.23) between young vs. older adults during the CPT trials. Our data demonstrate that 1) independent of age, sympathetic stimulation via CPT reduces parameters of ROV in the leg; and 2) the substantial reductions in leg ROV with aging does not appear to be explained by elevated sympathetic vasoconstrictor tone. Support or Funding Information Funded by NIH HL‐105467 (DPC)