Role of Alpha‐1 Adrenergic Vasoconstriction in Regulating Skeletal Muscle Blood Flow during Single Leg Knee Extension Exercise with Advancing Age

Abstract

Dynamic exercise evokes an increase in sympathetic nervous system (SNS) activity, a response that contributes to the “fine‐tuning” of blood flow to meet the metabolic demands of active skeletal muscle. Expression of this exercise‐induced increase in SNS activity is blunted within the vasculature of exercising muscle, an event known as “functional sympatholysis”. However, how this process may be altered with advancing age remains unclear. Therefore, the purpose of this study was to determine the role of alpha‐1 adrenergic vasoconstriction in the regulation of exercising skeletal muscle blood flow and the modulating effect of age. Eleven young (6 male, 27±1 yrs) and six older (6 male, 60±4 yrs) healthy volunteers participated in this study. Leg blood flow (LBF; ultrasound Doppler), mean arterial blood pressure (MAP), and leg vascular conductance (LVC) were evaluated at rest and during dynamic single‐leg knee‐extension exercise (0, 5, 10 and 15 W) before and after blood flow‐adjusted intra‐arterial administration of the alpha‐1 adrenergic agonist phenylephrine (PE, 0.03 ug·ml−1). At rest, there was no difference between young and older subjects in the PE‐induced decrease in LBF (−37±4% vs. −31±3%, young vs. older) or LVC (−53±6% vs. −48±2%, young vs. older). During exercise, the PE‐induced decrease in LBF was attenuated in an intensity‐dependent manner, but was not different between young (0W: −20±4%; 5W: −16±3%; 10W: −14±4%; 15W: −5±3%) and older (0W: −15±4%; 5W: −9±4%; 10W: −10±2%; 15W: −5±4%) subjects. Similarly, the PE‐induced decrease in LVC was attenuated as work rate increased, but was not different between groups at any work rate. MAP increased with exercise, but did not differ between groups or as a result of drug administration. Alpha‐1 adrenergic vasoconstriction was similar between young and older adults at rest and during low to moderate intensity knee‐extension exercise, suggesting that functional sympatholysis is not altered with advancing age.Support or Funding InformationThis project is funded in part by the National Institutes of Health (HL118313) and the U.S. Department of Veterans Affairs (RX001697, RX001418, E6910R).This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.