Influence of heat stress on exercise-induced changes in regional blood flow in sheep

Bell, A. W.; Hales, J. R. S.; King, Richard B.; Fawcett, A. A.

doi:10.1152/jappl.1983.55.6.1916

Cited by 78 publications

(41 citation statements)

References 21 publications

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“…Microsphere injections into the femoral artery and jugular vein, together with blood sampling from the pulmonary artery, enabled the calculation of the proportion of femoral blood flow passing through arteriovenous anastomoses (Hales, Fawcett & Bennett, 1978). It is unlikely that microsphere migration of any relevance to the present study would have occurred, since (a) monitoring radioactivity levels in the ear and lungs of rabbits for an 8 week period indicated no relocation of microspheres (Hales & Cliff, 1977), and (b) as previously discussed (Bell, Hales, King & Fawcett, 1983), no consistent trend was found in the blood flow values of any tissues of sheep subjected to three exercise periods at 48 h intervals.…”

Section: Experimental Protocolmentioning

confidence: 58%

Circulatory effects of a depilatory dose of mouse epidermal growth factor in sheep.

Carter

Fawcett

Hales

et al. 1988

The Journal of Physiology

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SUMMARY1. Haemodynamic parameters and tissue blood flow rates were measured in two groups of five sheep infused i.v. for 24 h with either saline or 128-6,g mouse epidermal growth factor (mEGF) kg-' body weight. Measurements were made preinfusion and at + 3, + 12, + 24, + 27 and + 48 h. We wished to assess relationships between blood flow rates and known functional changes in various organs during EGF treatment, especially any relationship between skin blood flow rate and the known depilatory effects of the protein in sheep.2. Cardiac output increased and total peripheral resistance and mean arterial pressure decreased during and after infusion in the mEGF-treated group relative to the control group.3. The greatest increase in blood flow rates occurred in woolled skin (+ 500 %) during mEGF infusion, a result which in itself may have been disparate with the known depilatory effects of EGF. The mucosas of the alimentary tract (except abomasum) and the submaxillary and sublingual salivary glands also showed vasodilatation.4. There were short-term increases in pituitary and adrenal gland blood flow that may have been associated with the corticotrophin-releasing factor properties of EGF. Flow in the thyroids showed the greatest increase post-infusion when thyroid hormone metabolism may have been reverting to normal. Blood flow rates decreased in the pancreas and perirenal fat. 5. Our general conclusion was that mEGF had specific vasodilator effects in the skin, the thyroid, submaxillary and sublingual glands and the mucosas of most of the alimentary tract.

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Section: Experimental Protocolmentioning

confidence: 58%

Circulatory effects of a depilatory dose of mouse epidermal growth factor in sheep.

Carter

Fawcett

Hales

et al. 1988

The Journal of Physiology

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“…Previous studies in humans (Kirwan et al 1987;Nielsen et al 1990Nielsen et al , 1993Nielsen et al , 1997, rats (Laughlin & Armstrong, 1983) and miniature swine (Armstrong et al 1987;McKirnan et al 1989) have shown that blood flow to active muscles is either maintained or increased when heat stress is superimposed during exercise. This is in contrast to the significant reductions in blood flow to some exercising muscles found in sheep with heat stress (Bell et al 1983). …”

Section: Discussionmentioning

confidence: 74%

Muscle blood flow is reduced with dehydration during prolonged exercise in humans

González‐Alonso

Calbet

Nielsen

1998

The Journal of Physiology

246

232

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The present study examined whether the blood flow to exercising muscles becomes reduced when cardiac output and systemic vascular conductance decline with dehydration during prolonged exercise in the heat. A secondary aim was to determine whether the upward drift in oxygen consumption (V̇O2) during prolonged exercise is confined to the active muscles. Seven euhydrated, endurance‐trained cyclists performed two bicycle exercise trials in the heat (35 °C; 40–50% relative humidity; 61 ± 2% of maximal V̇O2), separated by 1 week. During the first trial (dehydration trial, DE), they bicycled until volitional exhaustion (135 ± 4 min, mean ± s.e.m.), while developing progressive dehydration and hyperthermia (3.9 ± 0.3% body weight loss; 39.7 ± 0.2 °C oesophageal temperature, Toes). In the second trial (control trial), they bicycled for the same period of time while maintaining euhydration by ingesting fluids and stabilizing Toes at 38.2 ± 0.1 °C after 30 min exercise. In both trials, cardiac output, leg blood flow (LBF), vascular conductance and V̇O2 were similar after 20 min exercise. During the 20 min‐exhaustion period of DE, cardiac output, LBF and systemic vascular conductance declined significantly (8–14%; P < 0.05) yet muscle vascular conductance was unaltered. In contrast, during the same period of control, all these cardiovascular variables tended to increase. After 135 ± 4 min of DE, the 2.0 ± 0.6 l min−1 lower blood flow to the exercising legs accounted for approximately two‐thirds of the reduction in cardiac output. Blood flow to the skin also declined markedly as forearm blood flow was 39 ± 8% (P < 0.05) lower in DE vs. control after 135 ± 4 min. In both trials, whole body V̇O2 and leg V̇O2 increased in parallel and were similar throughout exercise. The reduced leg blood flow in DE was accompanied by an even greater increase in femoral arterial‐venous O2 (a‐vO2) difference. It is concluded that blood flow to the exercising muscles declines significantly with dehydration, due to a lowering in perfusion pressure and systemic blood flow rather than increased vasoconstriction. Furthermore, the progressive increase in oxygen consumption during exercise is confined to the exercising skeletal muscles.

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“…apparently greater than the pre-treatment activity of 200 IU/l), which was not present in sheep that walked for up to 3 h, without voluntarily stopping, no adverse consequences of the exercise treatment were found. Although exercise affected physiological variables in a predictable manner (Bell et al, 1983), the heart rate of the sheep at this speed of walking did not exceed 160 beats/min, the respiration rate was below 85 breaths/min, there was no evidence of dehydration (as determined by plasma osmolality) or hyperthermia (the rectal temperature of the sheep did not increase by more than 0.68C during exercise, and remained below 408C for most sheep). Therefore, a treatment regime of walking on a treadmill at 0.5 m/s at zero grade for up to 5 h or until a decrease in performance was observed was used in a replicated study.…”

Section: Treadmillmentioning

confidence: 86%

Behavioural and physiological measures following treadmill exercise as potential indicators to evaluate fatigue in sheep

Cockram

Murphy

Ringrose

et al. 2012

Animal

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The welfare consequences of long-distance transportation of animals remain a controversial topic. Animals that stand for most of the long journey (especially if additional muscular activity is required to deal with postural instability) are at risk of developing fatigue. Previous observational studies of behaviour and physiology suggested either that sheep do not become markedly fatigued by long journeys or that previous methods did not adequately identify fatigue. A range of behavioural and physiological measures were made on eight pairs of sheep during and after treadmill exercise. Within each pair of sheep, a treatment sheep was walked on a treadmill at 0.5 m/s for up to 5 h or until the sheep voluntarily stopped exercising or showed other signs of reduced performance, and a control sheep was exercised for two 10-min periods on either side of the exercise period for the treatment sheep. With the exception of one sheep that only walked for 4.5 h, all treatment sheep walked for 5 h without apparent difficulty. After exercise, the plasma cortisol concentration of treatment sheep was significantly greater than that of control sheep. However, there were no significant treatment effects on plasma creatine kinase activity or blood lactate concentration. After 5 h of exercise, there was a proportionate decrease in the median frequency of the electromyogram recorded over the m. semitendinosus, and this was significantly different from control sheep. There was no evidence that treatment sheep lay down sooner or for longer after treadmill exercise than controls. In sheep tested in a maze to examine whether there was increased motivation to rest after exercise, there was no significant difference between the times taken by treatment and control sheep to obtain a food reward. Qualitative behavioural assessment of the sheep by a panel of observers identified two main dimensions of sheep demeanour, but among descriptors elicited from observers only one person used a term associated with fatigue. No significant difference was found between the scores of treatment and control sheep on these two demeanour dimensions. Thus, there was little evidence that prolonged gentle walking exercise fatigues sheep. Further development of methods to both repeatedly induce and to identify fatigue in sheep is required.

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Influence of heat stress on exercise-induced changes in regional blood flow in sheep

Cited by 78 publications

References 21 publications

Circulatory effects of a depilatory dose of mouse epidermal growth factor in sheep.

Circulatory effects of a depilatory dose of mouse epidermal growth factor in sheep.

Muscle blood flow is reduced with dehydration during prolonged exercise in humans

Behavioural and physiological measures following treadmill exercise as potential indicators to evaluate fatigue in sheep

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