Rho-kinase inhibition improves haemodynamic responses and circulating ATP during hypoxia and moderate intensity handgrip exercise in healthy older adults

Abstract

Skeletal muscle haemodynamics and circulating adenosine triphosphate (ATP) responses during hypoxia and exercise are blunted in older (OA) vs. young (YA) adults, which may be associated with impaired red blood cell (RBC) ATP release. Rho-kinase inhibition improves deoxygenation-induced ATP release from OA isolated RBCs. We tested the hypothesis that Rho-kinase inhibition (via fasudil) in vivo would improve local haemodynamic and ATP responses during hypoxia and exercise in OA. Healthy YA (25 ± 3 years; n = 12) and OA (65 ± 5 years; n = 13) participated in a randomized, double-blind, placebo-controlled, crossover study on two days (≥5 days between visits). A forearm deep venous catheter was used to administer saline/fasudil and sample venous plasma ATP ([ATP]_V ). Forearm vascular conductance (FVC) and [ATP]_V were measured at rest, during isocapnic hypoxia (80% $S_{p{O}_2}$ ), and during graded rhythmic handgrip exercise that was similar between groups (5, 15 and 25% maximum voluntary contraction (MVC)). Isolated RBC ATP release was measured during normoxia/hypoxia. With saline, ΔFVC was lower (P < 0.05) in OA vs. YA during hypoxia (∼60%) and during 15 and 25% MVC (∼25-30%), and these impairments were abolished with fasudil. Similarly, [ATP]_V and ATP effluent responses from normoxia to hypoxia and rest to 25% MVC were lower in OA vs. YA and improved with fasudil (P < 0.05). Isolated RBC ATP release during hypoxia was impaired in OA vs. YA (∼75%; P < 0.05), which tended to improve with fasudil in OA (P = 0.082). These data suggest Rho-kinase inhibition improves haemodynamic responses to hypoxia and moderate intensity exercise in OA, which may be due in part to improved circulating ATP. KEY POINTS: Skeletal muscle blood flow responses to hypoxia and exercise are impaired with age. Blunted increases in circulating ATP, a vasodilator, in older adults may contribute to age-related impairments in haemodynamics. Red blood cells (RBCs) are a primary source of circulating ATP, and treating isolated RBCs with a Rho-kinase inhibitor improves age-related impairments in deoxygenation-induced RBC ATP release. In this study, treating healthy older adults systemically with the Rho-kinase inhibitor fasudil improved blood flow and circulating ATP responses during hypoxia and moderate intensity handgrip exercise compared to young adults, and also tended to improve isolated RBC ATP release. Improved blood flow regulation with fasudil was also associated with increased skeletal muscle oxygen delivery during hypoxia and exercise in older adults. This is the first study to demonstrate that Rho-kinase inhibition can significantly improve age-related impairments in haemodynamic and circulating ATP responses to physiological stimuli, which may have therapeutic implications.

Keywords: ATP; ageing; blood flow; exercise; fasudil; hypoxia.