Modulation of postjunctional α‐adrenergic vasoconstriction during exercise and exogenous ATP infusions in aging humans

The ability to modulate α‐adrenergic vasoconstriction in contracting muscle is impaired with age. In young adults, adenosine triphosphate (ATP) has been shown to inhibit vasoconstrictor responsiveness similar to exercise. We tested the hypothesis that modulation of postjunctional α‐adrenergic vasoconstriction to exogenous ATP is impaired in aging humans. We measured forearm blood flow (FBF; Doppler ultrasound) and calculated vascular conductance (FVC) to intra‐arterial infusions of phenylephrine (α 1 ‐agonist) and dexmedetomidine (α 2 ‐agonist) during rhythmic handgrip exercise (15% MVC), a control non‐exercise vasodilator condition (adenosine), and ATP infusion in 7 young (22±1) and 7 older (64±3 yrs) adults. Forearm hyperemia was matched across all conditions. During adenosine, forearm vasoconstrictor responses to direct α 1 ‐stimulation were lower in older adults (ΔFVC= −25±3 vs −41±5%); the responses to α 2 ‐stimulation were not different (−38±5% vs −44±7%). The ability to blunt α 1 ‐ and α 2 ‐vasoconstriction was impaired in older adults during exercise (α 1 = 31±9 vs 74±8%; α 2 = 28±10 vs 60±10%). In contrast, ATP reduced the vasoconstrictor responses by ~85–90% in both age groups. We conclude that the sympatholytic effect of exogenous ATP is not reduced with age, and thus blunted ATP release during exercise may contribute to the impaired exercise sympatholysis in older adults. Supported by HL‐087952