Repeated increases in blood flow, independent of exercise, enhance conduit artery vasodilator function in humans

Abstract

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 men immersed their forearms in water at 42°C for three 30-min sessions/wk across 8 wk. 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 Ͻ 0.001) and shear rate (P Ͻ 0.001) in the uncuffed forearm; this response was attenuated in the cuffed limb (P Ͻ 0.005). Repeated episodic exposure to bilateral heating induced an increase in endothelium-dependent vasodilation in response to 5-min ischemic (P Ͻ 0.05) and ischemic handgrip exercise (P Ͻ 0.005) stimuli in the uncuffed forearm, whereas the 8-wk 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 that enhance endothelium-mediated vasodilator function in humans. These findings reinforce the importance of the direct impacts of shear stress on the vascular endothelium in humans.

Combined aerobic and resistance exercise training decreases peripheral but not central artery wall thickness in subjects with type 2 diabetes

“…When looking at functional as opposed to structural outcome measures, a large number of previous studies in animals (Langille et al 1989;Langille and O'Donnell 1986) and humans (Tinken et al 2010;Rowley et al 2011) have identified shear stress as the key stimulus for localised adaptation in conduit arteries. For example, recent studies in humans found that that adaptation in BA function as measured by flow mediated dilation in response to 8-weeks exercise training (Birk et al 2012;Tinken et al 2010) or heat exposure (Naylor et al 2011) are abolished in the contra-lateral arm when the increases in shear rate are mitigated by subdiastolic cuff inflation. Interestingly, when a similar design was used to examine the importance of the shear rate stimulus for adaptation in wall thickness, the abolished shear stimulus did not prevent the decreases in BA WT across 8-weeks of handgrip training (Thijssen et al 2011a).…”

Impact of 2‐Weeks Continuous Increase in Retrograde Shear Stress on Brachial Artery Vasomotor Function in Young and Older Men

“…Several studies have explored the impact of repeated exposure to elevations in antegrade shear stress via training, heating, or in vitro manipulation of antegrade shear 7, 13, 14, 15, 16, 17. These studies consistently report a dose‐dependent increase in arterial caliber and improvement in endothelial function, possibly through upregulation of endothelial nitric oxide synthase 1, 18.…”

PGC-1α Mediated Muscle Aerobic Adaptations to Exercise, Heat and Cold Exposure

“…This is inferred from recent studies that have demonstrated that heat stress may result in similar muscle adaptations to that observed following endurance exercise (Harris et al, 2003;Hooper, 1999;Liu & Brooks, 2012;Naylor et al, 2011;Yamaguchi et al, 2010). For instance, mild heat stress (39-40°C) has been shown to increase PGC-1α activity and induce PGC-1α mRNA and protein expression in a variety of muscle cell lines (Liu & Brooks, 2012;Yamaguchi et al, 2010), in addition to an increase in the mRNA content of key mitochondrial transcription factors (NRF1, NRF2 and Tfam), complex-IV subunits (COX2 and COX4) as well as glucose transporter 4 (GLUT4) mRNA (Liu & Brooks, 2012).…”

“…The production of metabolic heat during exercise appears to have a role in muscle oxidative phenotype transformations (Harris et al, 2003;Hooper, 1999;Liu & Brooks, 2012;Naylor et al, 2011;Yamaguchi et al, 2010). This is inferred from recent studies that have demonstrated that heat stress may result in similar muscle adaptations to that observed following endurance exercise (Harris et al, 2003;Hooper, 1999;Liu & Brooks, 2012;Naylor et al, 2011;Yamaguchi et al, 2010).…”

“…In humans, heat exposure has shown to induce adaptations where PGC-1α may potentially be involved (Michael et al, 2001;Prior et al, 2004). These adaptations include decreases in resting blood glucose concentration, improved brachial artery function and remodelling (Hooper, 1999;Naylor et al, 2011). Oct 2014 ‫|‬ Volume 3 ‫|‬ Issue 1 ‫|‬ e7…”