The Effect of Exogenous Adenosine Triphosphate on Blood Flow Kinetics During Dynamic Forearm Exercise

Abstract

IntroductionAdenosine triphosphate (ATP) is a vasodilating metabolite that plays a role in exercise hyperemia. In humans, exogenous infusion of ATP elevates skeletal muscle blood flow values to that observed during moderate‐intensity exercise. Recently ATP has been shown to evoke prolonged vasodilation over 150 minutes without tachyphylaxis. However, the steady‐state hyperemic responses to superimposed forearm exercise remain unaltered. The kinetics of blood flow during the initiation of exercise remains not well understood. Therefore we evaluated the effects of prolonged exogenous infusion of ATP on exercise hyperemia during the transition between rest and initiation of exercise.MethodsWhile supine, eight healthy young participants (4M/4F; 25±1 years) performed 5 minutes of rhythmic dynamic handgrip exercise bouts (20% of maximum), first during saline (control), then at minute 5 and minute 150 during a continuous ATP infusion into the brachial artery. Each duty cycle consisted of 1 second contraction and 2 second relaxation. Mean blood velocity (MBV; cm/s), forearm vascular conductance (FVC; ml/minutes/100 mmHg), and shear rate (8*MBV/diameter; seconds−1) were calculated. The kinetics at the onset of exercise was assessed by calculating the slope of the FVC responses for the first 20 duty cycles after the start of contractions. Data are presented as means ± SEM.ResultsDuring saline control FVC was 3.9±0.3 at rest and with exercise rose to 22.7±0.84 and 27.8±1.2 ml/minute/100mmHg at 30 seconds and 1 minute, respectively (P<0.05 for both). Infusion of ATP increased FVC (3.9±0.3 vs 43.1±2.0 ml/minutes/100 mmHg, P<0.05) at five minutes and to 61.0±1.1 ml/minutes/100 mmHg at 150 minutes (P<0.05) with no systemic hemodynamic changes. Prolonged infusion of ATP did not alter the kinetics at the onset of contractions over 20 duty cycles of exercise hyperemic responses compared to control (0.71±0.1 control vs 1.01±0.1 ml/minutes/100mmHg/cycle at 5 minutes and vs 0.65±0.1 at 150 minutes, P>0.05 for all). Shear rate significantly increased compared to control (92±5 vs 751±57 seconds−1, P<0.05) but was not different across exercise responses during ATP infusion (751±57 at 5 minutes vs 549±46 seconds−1 at 150 minutes, P>0.05).ConclusionsOur findings demonstrate that despite the ability of ATP to elevate blood flow to that observed during exercise, the blood flow kinetics for the initiation of dynamic exercise hyperemic response are unaffected and remain unaltered after 150 minutes of prolonged ATP infusion. Further investigation in needed to understand the role of ATP in regulating the blood flow kinetics during dynamic exercise in humans.Support or Funding InformationThis research was supported by National Institutes of Health Research Grants HL‐119337 and by CTSA UL1 TR000135. The Caywood Professorship via the Mayo Foundation also supported this study.