This study aimed to determine the importance of repeated increases in blood flow to conduit artery adaptation, using an exercise-independent repeated episodic stimulus. Recent studies suggest that exercise training improves vasodilator function of conduit arteries via shear stress-mediated mechanisms. However, exercise is a complex stimulus that may induce shear-independent adaptations. Nine healthy males immersed their forearms in water at 42°C for three 30min sessions/week across 8 weeks. During each session, a pneumatic pressure cuff was inflated around one forearm to unilaterally modulate heating-induced increases in shear. Forearm heating was associated with an increase in brachial artery blood flow (P < 0.001) and shear rate (P<0.001) in the uncuffed forearm; this response was attenuated in the cuffed limb (P<0.005). Repeated episodic exposure to bilateral heating induced an increase in endothelium-dependent vasodilation in response to 5-min ischaemic (P<0.05) and ischaemic handgrip exercise (P<0.005) stimuli in the uncuffed forearm, whereas the 8-week heating intervention did not influence dilation to either stimulus in the cuffed limb. Endothelium-independent glyceryl trinitrate responses were not altered in either limb. Repeated heating increases blood flow to levels which enhance endothelium-mediated vasodilator function in humans. These findings reinforce the importance of direct impacts of shear stress on the vascular endothelium in humans.
- nitric oxide
- shear stress
- Copyright © 2010, American Journal of Physiology - Heart and Circulatory Physiology