Modulation of muscle sympathetic nerve activity to muscle heating during dynamic exercise

Cook, Jonathan S.; Ray, Chester A.

doi:10.1152/ajpregu.90823.2008

Cited by 3 publications

(2 citation statements)

References 30 publications

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“…However, flow to the locomotory muscles in the leg and tail remained constant during the heating and cooling cycle. The effect of exercise on blood flow overrides any temperature effect in human skeletal muscle, and muscle blood flow increases with exercise but does not differ between muscles at 33-34 and 37-38°C (Ferguson et al, 2006;Cook and Ray, 2009). In cane toads, total blood flow in the systemic artery during exercise is similar at 20 and 30°C (Hedrick et al, 1999), so that there is no temperatureinduced central limitation to tissue blood flow over that temperature range.…”

Section: Discussionmentioning

confidence: 97%

Physiology of invasion: cane toads are constrained by thermal effects on physiological mechanisms that support locomotor performance

Seebacher

Franklin

2011

Journal of Experimental Biology

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SUMMARYUnderstanding the mechanisms that constrain the invasiveness of introduced animals is essential for managing invasions and for predicting their limits. In most vertebrate species, the capacity for invasion relies upon the physiological systems that support locomotion, and oxygen transport and metabolism may become limiting as environmental temperatures increase as predicted by the oxygen limitation hypothesis. Here we test the oxygen limitation hypothesis and propose the alternative hypothesis that within-individual plasticity will compensate for thermal variation. We show that during exercise in the invasive cane toad (Rhinella marina) oxygen transport by the cardiovascular system was maximised in warm-acclimated toads at high (30°C) temperatures, and that oxygen content of arterial blood was not affected by temperature. Resting oxygen consumption remained stable across a 10°C temperature range (20-30°C) when toads were allowed to acclimate, so that there was no increase in resting oxygen demand that could lead to a decrease in aerobic scope at high temperatures. Additionally, temperature acclimation had no effect on arterial-venous differences in oxygen partial pressures. Toads relied more on glycolytic ATP production at low temperatures to support locomotor activity. Mitochondrial capacities (citrate synthase and cytochrome c oxidase activities) were greatest at warmer temperatures. Interestingly, the metabolic cost of exercise increased at low temperatures. In contradiction to predictions by the oxygen limitation hypothesis, aerobic performance was not limited by high temperatures. On the contrary, the relatively slow advance of cane toads to cooler climates can be explained by the constraints of low temperatures on the physiological systems supporting locomotion. It is likely that human-induced global warming will facilitate invasions of environments that are currently too cool to support cane toads. Supplementary material available online at

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Section: Discussionmentioning

confidence: 97%

Physiology of invasion: cane toads are constrained by thermal effects on physiological mechanisms that support locomotor performance

Seebacher

Franklin

2011

Journal of Experimental Biology

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“…To our knowledge, the current data are the first report of RBV and RVRI in response to IFRHG. IFRHG is considered to be a similar yet distinct stimulus compared to rhythmic handgrip exercise under freely perfused conditions (Cook and Ray ). Herein, we demonstrated an ~40% increase in RVRI at peak exercise and a 25–35% increase in RVRI during PHGCA, relative to pre‐exercise baseline.…”

Section: Discussionmentioning

confidence: 99%

Effect of oxidative stress on sympathetic and renal vascular responses to ischemic exercise

et al. 2013

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Reactive oxygen species (ROS), produced acutely during skeletal muscle contraction, are known to stimulate group IV muscle afferents and accentuate the exercise pressor reflex (EPR) in rodents. The effect of ROS on the EPR in humans is unknown. We conducted a series of studies using ischemic fatiguing rhythmic handgrip to acutely increase ROS within skeletal muscle, ascorbic acid infusion to scavenge free radicals, and hyperoxia inhalation to further increase ROS production. We hypothesized that ascorbic acid would attenuate the EPR and that hyperoxia would accentuate the EPR. Ten young healthy subjects participated in two or three experimental trials on separate days. Beat-by-beat measurements of heart rate (HR), mean arterial pressure (MAP), muscle sympathetic nerve activity (MSNA), and renal vascular resistance index (RVRI) were measured and compared between treatments (saline and ascorbic acid; room air and hyperoxia). At fatigue, the reflex increases in MAP (31 ± 3 versus 29 ± 2 mmHg), HR (19 ± 3 versus 20 ± 3 bpm), MSNA burst rate (21 ± 4 versus 23 ± 4 burst/min), and RVRI (39 ± 12 versus 44 ± 13%) were not different between saline and ascorbic acid. Relative to room air, hyperoxia did not augment the reflex increases in MAP, HR, MSNA, or RVRI in response to exercise. Muscle metaboreflex activation and time/volume control experiments similarly showed no treatment effects. While contrary to our initial hypotheses, these findings suggest that ROS do not play a significant role in the normal reflex adjustments to ischemic exercise in young healthy humans.

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Interactive effect of aging and local muscle heating on renal vasoconstriction during isometric handgrip

Kuipers

Sauder²,

Kearney³

et al. 2009

American Journal of Physiology-Renal Physiology

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The purpose of the study was to determine the interactive effect of aging and forearm muscle heating on renal vascular conductance and muscle sympathetic nerve activity (MSNA) during ischemic isometric handgrip. A tube-lined, water-perfused sleeve was used to heat the forearm in 12 young (27 +/- 1 yr) and 9 older (63 +/- 1 yr) subjects. Ischemic isometric handgrip was performed before and after heating. Muscle temperature (intramuscular thermistor) was 34.3 +/- 0.2 and 38.7 +/- 0.1 degrees C during normothermia and heating, respectively. At rest, heating had no effect on renal blood velocity (Doppler ultrasound) or renal vascular conductance in either group (young, n = 12; older, n = 8). Heating compared with normothermia caused a significantly greater increase in renal vasoconstriction during exercise and postexercise muscle ischemia (PEMI) in both groups. However, the increase in renal vasoconstriction during heating was greater in the older compared with the young subjects (18 +/- 3 vs. 8 +/- 3%). During handgrip, heating elicited greater increases in MSNA responses in the older group (young, n = 12; older, n = 6), whereas no statistical difference was observed between groups during PEMI. In summary, aging augments renal vascular responses to ischemic isometric handgrip during heating of the exercising muscle. The greater renal vasoconstriction was associated with augmented MSNA in the older subjects.

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Modulation of muscle sympathetic nerve activity to muscle heating during dynamic exercise

Cited by 3 publications

References 30 publications

Physiology of invasion: cane toads are constrained by thermal effects on physiological mechanisms that support locomotor performance

Physiology of invasion: cane toads are constrained by thermal effects on physiological mechanisms that support locomotor performance

Effect of oxidative stress on sympathetic and renal vascular responses to ischemic exercise

Interactive effect of aging and local muscle heating on renal vasoconstriction during isometric handgrip

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