title: Sympathetic nervous system activation reduces contraction-induced rapid vasodilation in the leg of humans independent of age.
abstract: Contraction-induced rapid vasodilation is attenuated similarly in the upper and lower limbs of older adults. In the forearm, this attenuation is in part due to a greater sympathetic vasoconstriction. We examined whether the age-related reduction in contraction-induced vasodilation in the leg is also due to a sympathetic vasoconstrictive mechanism. Thirteen young (24 ± 1 yr) and twelve older adults (67 ± 1 yr) performed single-leg knee extension at 20 and 40% of work-rate maximum (WRmax) during control and cold-pressor test (CPT) conditions. Femoral artery diameter and blood velocity were measured using Doppler ultrasound. Vascular conductance (VC; ml·min-1·mmHg-1) was calculated using blood flow (ml/min) and mean arterial pressure (mmHg). Peak (ΔVC from baseline) and total VC were blunted in older adults during control conditions across exercise intensities (P< 0.05). Peak and total VC were reduced during CPT in both age groups across exercise intensities (P< 0.05). The relative change (i.e., %reduction; CPT vs. control) in peak (-25 ± 5 vs. -22 ± 4% at 20% WRmax; and -21 ± 6 vs. -27 ± 5% at 40% WRmax;P= 0.42-0.55) and total VC (-28 ± 5 vs. -36 ± 6% at 20% WRmax; and -22 ± 8 vs. -33 ± 5% at 40% WRmax;P= 0.23-0.34) were similar between young and older adults. When matched for absolute workload (~10 W), age differences persisted in peak VC (P< 0.05) under both conditions, with similar relative changes in peak and total VC during CPT. Our data suggest that1) sympathetic stimulation reduces contraction-induced rapid vasodilation in the leg of young and older adults similarly; and2) enhanced sympathetic vasoconstriction does not fully explain age-related differences in contraction-induced vasodilation within the leg.NEW & NOTEWORTHYAging is associated with attenuated contraction-induced rapid onset vasodilation (ROV). Within the forearm, this attenuation is partially due to enhanced sympathetic vasoconstriction. In the current study, we found that sympathetic vasoconstriction reduces contraction-induced ROV within the leg of both young and older adults, with the magnitude of change being similar between age groups. Our current results suggest that age-related attenuations in contraction-induced ROV within the leg are not fully explained by a sympathetic vasoconstrictor mechanism.
authors.affiliation: Department of Physical Therapy and Rehabilitation Science, Carver College of Medicine, University of Iowa, Iowa City, Iowa.
authors.forename: William E
authors.initials: WE
authors.lastname: Hughes
authors.affiliation: Department of Physical Therapy and Rehabilitation Science, Carver College of Medicine, University of Iowa, Iowa City, Iowa.|Abboud Cardiovascular Research Center, Carver College of Medicine, University of Iowa, Iowa City, Iowa; and.
authors.forename: Nicholas T
authors.initials: NT
authors.lastname: Kruse
authors.affiliation: Department of Physical Therapy and Rehabilitation Science, Carver College of Medicine, University of Iowa, Iowa City, Iowa; darren-casey@uiowa.edu.|Abboud Cardiovascular Research Center, Carver College of Medicine, University of Iowa, Iowa City, Iowa; and.|Fraternal Order of Eagles Diabetes Research, Carver College of Medicine, University of Iowa, Iowa City, Iowa.
authors.forename: Darren P
authors.initials: DP
authors.lastname: Casey
mesh_terms: D000328:Adult; D000368:Aged; D005260:Female; D006801:Humans; D007866:Leg / Q000098:blood supply* / Q000502:physiology*; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D011897:Random Allocation; D013564:Sympathetic Nervous System / Q000502:physiology*; D014661:Vasoconstriction / Q000502:physiology; D014664:Vasodilation / Q000502:physiology*
keywords: contraction-induced rapid vasodilation; leg; sympathetic vasoconstriction