Skeletal muscle reactive oxygen species and microvascular endothelial function in age-related hypertension: a study protocol using a microdialysis technique.

Increased reactive oxygen species (ROS) generation and microvascular endothelial disruptions occur with natural ageing, but often transpire before the detection of cardiometabolic conditions including hypertension. Age-related increases in blood pressure are driven by complex systemic changes with poorly understood integrated mechanisms. The deconditioning experienced by ageing skeletal muscle from mid-life is associated with reduced microvascular blood flow and increased peripheral resistance, suggesting that vasodilatory decrements in the muscle may precede the age-related increases in blood pressure. Structural and functional changes within the vascular and skeletal muscle systems with advancing age can influence redox homeostasis, and vice versa, further compounding microvascular endothelial dysfunction. Therefore, comparisons between the microvascular environments of healthy and hypertensive cohorts can provide insights into the changes that occur during significant periods of functional decline. This comprehensive study protocol describes a microdialysis technique to assess the interactions of microvascular health and functional changes in the muscle, which currently cannot be otherwise addressed. Here, we detail an experimental protocol to simultaneously detect skeletal muscle ROS (H₂O₂ and indirect O₂ ^-), determine nutritive blood flow and assess microvascular endothelial function in response to acetylcholine stimulation. We expect that healthy middle-aged individuals should not have increased ROS generation in the muscle at rest, compared to their hypertensive or older counterparts, but may exhibit perturbed microvascular function. The described technique allows for intricate exploration of microvascular physiology that will provide a critically novel insight into benchmarking potential age-related mechanisms involved in the development of age-related hypertension, and aid in early identification and prevention. KEY POINTS: Increased reactive oxygen species (ROS) production and microvascular endothelial dysfunction precede the onset of age-related cardiometabolic and vascular conditions such as hypertension. The profound structural and functional changes that occur within the vasculature and in skeletal muscle from middle age prompt a need to mechanistically explore the microvascular environment in healthy and hypertensive individuals. Using a novel microdialysis technique, we detail an experimental protocol to simultaneously detect skeletal muscle ROS (H₂O₂ and indirect O₂ ^-), determine nutritive blood flow and assess microvascular endothelial function in response to acetylcholine stimulation. With this technique and study protocol, we can reveal functional insights into potential perturbations in ROS generation at rest and the microvascular endothelium, which play important roles in the development of age-related hypertension.