Rho‐kinase Inhibition Improves Hemodynamic Responses and Circulating ATP During Hypoxia and Exercise in Healthy Older Adults
Authors: Racine Matthew L. , Terwoord Janée D. , Ketelhut Nathan B. , Bachman Nate P. , Richards Jennifer C. , Luckasen Gary J. , Dinenno Frank A. 
Published: June 2021

Circulating ATP is a potent vasodilator believed to assist in the matching of tissue oxygen delivery to oxygen demand. Older adults have impaired skeletal muscle hemodynamic responses to hypoxia and exercise and blunted increases in circulating ATP during these stimuli, which may be due to reduced deoxygenation‐mediated red blood cell (RBC) ATP release. We recently demonstrated that treatment of isolated RBCs with a Rho‐kinase inhibitor improves RBC membrane deformability and restores ATP release from RBCs of older adults. Thus, the goal of the present study was to test the hypothesis that in vivo Rho‐kinase inhibition would improve hemodynamic responses and circulating ATP during hypoxia and exercise in older adults. Healthy young (Y; 27 ± 1 years; n = 5) and older (O; 67 ± 2 years; n = 7) adults participated in a double‐blind, randomized, placebo‐controlled, crossover design study on two days (≥ 5 days between visits). A deep venous catheter in the forearm was used to administer the placebo (100 ml saline/60 min) or the Rho‐kinase inhibitor (60 mg fasudil/60 min) and to sample blood for plasma [ATP]. Forearm vascular conductance (FVC; mean arterial pressure from finometry and forearm blood flow (FBF) from Doppler ultrasound) was calculated at rest, during 5 min of isocapnic hypoxia (80% SpO2), and during graded intensity rhythmic handgrip exercise at 5, 15 and 25% of maximum voluntary contraction (MVC; 4 min per workload). Plasma [ATP] was measured at rest and at the end of each condition, and RBCs were isolated to measure ATP release in response to normoxic (PO2 ~120 mmHg) and hypoxic (PO2 ~24 mmHg) stimuli using the luciferin‐luciferase technique. In the placebo trial, the increase in FVC during hypoxia was ~50% lower in O vs Y, and during exercise the greatest age impairment occurred at 25% MVC (266.4 ± 27.6 vs 394.9 ± 35.0 ml/min/100 mmHg; P < 0.05). Plasma [ATP] and ATP effluent (FBF × [ATP]; an index of the total circulating rate of ATP) tended to be lower in O vs Y during hypoxia (75.3 ± 16.6 vs 100.6 ± 18.8 nmol/L and 2.3 ± 0.7 vs 3.1 ± 0.7 nmol/min, respectively) and were lower at 25% MVC (92.8 ± 12.6 vs 168.7 ± 31.5 nmol/L and 28.1 ± 4.9 vs 66.9 ± 9.6 nmol/min, respectively; P < 0.05). The increase in isolated RBC ATP release from normoxia to hypoxia was also impaired in O vs Y (21.4 ± 17.2% vs 77.8 ± 13.3%; P < 0.05). Compared to control, fasudil in O improved FVC during hypoxia (35.2 ± 3.7 ml/min/100 mmHg; P < 0.05) and 25% MVC exercise (324.4 ± 21.7 ml/min/100 mmHg; P < 0.05), and abolished the impairment vs Y. Fasudil tended to improve plasma [ATP] and ATP effluent during hypoxia in O (98.7 ± 29.0 nmol/L and 3.34 ± 0.8 nmol/min), and during 25% MVC exercise (152.2 ± 26.7 nmol/L and 48.3 ± 6.7 nmol/min). Fasudil also tended to improve isolated RBC ATP release (55.6 ± 17.5% vs 21.4 ± 17.2%) and abolished the impairment vs Y. These preliminary data suggest that in vivo Rho‐kinase inhibition improves hemodynamic responses to hypoxia and exercise in older adults, and that this may be related to elevated circulating ATP.Support or Funding InformationHL119337, F31HL126377This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.