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Am J Physiol Heart Circ Physiol 296: H497-H504, 2009. First published December 5, 2008; doi:10.1152/ajpheart.01016.2008
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Role of {alpha}1-adrenergic vasoconstriction in the regulation of skeletal muscle blood flow with advancing age

D. Walter Wray,1,2,4 Steven K. Nishiyama,1 and Russell S. Richardson1,2,3,4

1Department of Medicine, University of California, San Diego, La Jolla, California; 2Department of Internal Medicine, Division of Geriatrics, and 3Department of Exercise and Sport Science, University of Utah, and 4Geriatric Research and Clinical Center, Salt Lake City Veterans Affairs Medical Center, Salt Lake City, Utah

Submitted 18 September 2008 ; accepted in final form 27 November 2008

{alpha}1-Adrenergic vasoconstriction during dynamic leg exercise is diminished in younger individuals, although the extent of this exercise-induced "sympatholysis" in the elderly remains uncertain. Thus, in nine young (25 ± 1 yr) and six older (72 ± 2 yr) healthy volunteers, we evaluated changes in leg blood flow (ultrasound Doppler) during blood flow-adjusted intra-arterial infusion of phenylephrine (PE; a selective {alpha}1-adrenergic agonist) at rest and during knee-extensor leg exercise at 20, 40, and 60% of maximal work rate (WRmax). To probe the potential contributors to exercise-induced changes in {alpha}1-adrenergic receptor sensitivity, exercising leg O2 consumption (VO2) and lactate efflux were also evaluated (n = 10). At rest, the PE-induced vasoconstriction (i.e., decrease in leg blood flow) was diminished in older (–37 ± 3%) compared with young (–54 ± 4%) subjects. During exercise, the magnitude of {alpha}1-adrenergic vasoconstriction in the active leg decreased in both groups. However, compared with young, older subjects maintained a greater vasoconstrictor response to PE at 40% WRmax (–14 ± 3%, older; –7 ± 2%, young) and 60% WRmax (–11 ± 3%, older; –4 ± 3%, young). It is possible that this observation may be attributed to lower absolute work rates in the older group, because, for a similar absolute work rate ({approx}10 W) and leg VO2 ({approx}0.36 l/min), vasoconstriction to PE was not different between groups (–14 ± 3%; older; –17 ± 5%, young). Together, these data challenge the concept of reduced sympatholysis in the elderly, suggesting instead that the inhibition of {alpha}1-adrenergic vasoconstriction in the exercising leg is associated with work performed and, therefore, more closely related to the rate of oxidative metabolism than to age per se.

aging; ultrasound Doppler; exercise


Address for reprint requests and other correspondence: D. W. Wray, Dept. of Internal Medicine, Division of Geriatrics, Univ. of Utah, VAMC SLC, Bldg. 2, 1C03, 500 Foothill Dr., Salt Lake City, UT 84132 (e-mail: walter.wray{at}hsc.utah.edu)






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