Experimental physiology
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Experimental physiology · Feb 2017
Elevated skin and core temperatures both contribute to reductions in tolerance to a simulated haemorrhagic challenge.
What is the central question of this study? Combined increases in skin and core temperatures reduce tolerance to a simulated haemorrhagic challenge. The aim of this study was to examine the separate and combined influences of increased skin and core temperatures upon tolerance to a simulated haemorrhagic challenge. What is the main finding and its importance? Skin and core temperatures increase during many occupational settings, including military procedures, in hot environments. ⋯ The lowest LBNP tolerance was observed during combined skin and core hyperthermia (257 ± 106 mmHg min; P < 0.05 relative to all other trials). These data indicate that elevated skin temperature, as well as elevated core temperature, can both contribute to reductions in LBNP tolerance in heat-stressed individuals. However, heat stress-induced reductions in LBNP tolerance are greatest in conditions when both skin and core temperatures are elevated.
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Experimental physiology · Feb 2017
Butyrate stimulates adipose lipolysis and mitochondrial oxidative phosphorylation through histone hyperacetylation-associated β3 -adrenergic receptor activation in high-fat diet-induced obese mice.
What is the central question of this study? Butyrate can prevent diet-induced obesity through increasing energy expenditure. However, it is unclear whether β3 -adrenergic receptors (ARβ3) mediate butyrate-induced adipose lipolysis. What is the main finding and its importance? Short-term oral administration of sodium butyrate is effective in alleviating diet-induced obesity through activation of ARβ3-mediated lipolysis in white adipose tissue. ⋯ The G protein-coupled receptor 43 and p-CREB (Ser133) were significantly stimulated by SB. In addition, an active transcription marker, H3K9Ac, was significantly enriched on the promoter of the ARβ3 gene. Our results indicate that short-term oral administration of SB is effective in alleviating diet-induced obesity through activation of the ARβ3-mediated lipolysis in the epididymal white adipose tissue.
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Experimental physiology · Feb 2017
Effects of early and delayed initiation of exercise training on cardiac and haemodynamic function after spinal cord injury.
What is the central question of this study? How does early versus delayed initiation of passive hindlimb cycling, as well as detraining, affect cardiac function and blood pressure control in a rodent model of spinal cord injury? What is the main finding and its importance? Early or delayed initiation of hindlimb cycling improves cardiac and haemodynamic function in spinal cord injury, although the benefits of early administration are more pronounced. We also demonstrate the need for exercise to be maintained, because detraining rapidly reverses the cardiac and haemodynamic benefits. Spinal cord injury (SCI) reduces physical activity and alters descending supraspinal cardiovascular control, predisposing this population to early onset of cardiovascular disease. ⋯ Between weeks 7 and 9 post-SCI, the no PHLC/delayed PHLC rats exhibited fewer spontaneous AD events than the early PHLC/detraining rats (P < 0.01). We show, for the first time, that delayed exercise promotes similar improvements in cardiac and haemodynamic function to those observed with early initiation. Furthermore, exercise needs to be maintained, because detraining reduces these cardiohaemodynamic benefits.
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Experimental physiology · Dec 2016
Effects of fatigue on corticospinal excitability of the human knee extensors.
What is the central question of this study? Do group III and IV muscle afferents act at the spinal or cortical level to affect the ability of the central nervous system to drive quadriceps muscles during fatiguing exercise? What is the main finding and its importance? The excitability of the motoneurone pool of vastus lateralis was unchanged by feedback from group III and IV muscle afferents. In contrast, feedback from these afferents may contribute to inhibition at the cortex. However, the excitability of the corticospinal pathway was not directly affected by feedback from these afferents. ⋯ Likewise, after the 2-min knee flexor MVC, maintained firing of these afferents showed no effect on vastus lateralis MEPs or TMEPs (P = 0.69 and P = 0.34, respectively). Motoneurones of vastus lateralis do not become less excitable during fatiguing isometric MVCs. Moreover, fatigue-sensitive group III/IV muscle afferents fail to affect the overall excitability of vastus lateralis motoneurones during MVCs.
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Experimental physiology · Dec 2016
Quantifying cerebrovascular reactivity in anterior and posterior cerebral circulations during voluntary breath holding.
What is the central question of this study? We developed and validated a 'stimulus index' (SI; ratio of end-tidal partial pressures of CO2 and O2 ) method to quantify cerebrovascular reactivity (CVR) in anterior and posterior cerebral circulations during breath holding. We aimed to determine whether the magnitude of CVR is correlated with breath-hold duration. What is the main finding and its importance? Using the SI method and transcranial Doppler ultrasound, we found that the magnitude of CVR of the anterior and posterior cerebral circulations is not positively correlated with physiological or psychological break-point during end-inspiratory breath holding. ⋯ There were significant inverse but modest relationships between both MCAv and PCAv CVR and both physiological and psychological break-points (r < -0.53, P < 0.03). However, these relationships were absent when MCAv and PCAv cerebrovascular conductance reactivity was correlated with both physiological and psychological break-points (r > -0.42; P > 0.06). Although central chemoreceptor activation is likely to be contributing to break-point, our data suggest that CVR-mediated CO2 washout from central chemoreceptors plays no role in determining break-point, probably because of a reduced arterial-to-tissue CO2 gradient during breath holding.