Mechanism of enhanced cold tolerance by an ephedrine-caffeine mixture in humans

Vallerand, A. L.; Jacobs, Ira; Kavanagh, Mélanie

doi:10.1152/jappl.1989.67.1.438

Cited by 32 publications

(14 citation statements)

References 20 publications

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“…Cold stress is a powerful stimulus for sympathetic nervous system (SNS) activation in man, as reflected in the increased concentration of noradrenaline (Johnson, Hayward, Jacobs, Collis, Eckerson & Williams, 1977). In the present study, the -7-fold increase in this catecholamine reflected the strong adrenergic drive for vasoconstriction in the body shell, and is equivalent to (Vallerand et al 1988;Vallerand & Jacobs, 1990), or greater (MacNaughton et al 1990Vallerand, Jacobs & Kavanagh, 1989) than, the values quoted in earlier cold air exposure studies. Consistent with the majority of previous cold stress studies (including cold water immersion), the present study found no cold-induced increase in adrenaline concentration.…”

Section: Physiological Responses To Moderate Cold Stresssupporting

confidence: 41%

Physiological responses to moderate cold stress in man and the influence of prior prolonged exhaustive exercise

Weller¹,

Greenhaff²,

Macdonald³

1998

Experimental Physiology

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SUMMARYA study was undertaken in man to investigate whether during moderate cold stress, the proportion of carbohydrate (CHO) oxidized is increased, and whether prior prolonged exhaustive exercise compromises thermoregulation. Eight euglycaemic men were cooled by a liquid-conditioned suit (1) after an overnight fast (Con) and (2) -2 h after an exercise protocol in which CHO availability was substantially lowered (Post-Ex). The cooling stimulus lasted 90 min (Cooling) and was preceded by a 30 min thermo-neutral baseline phase (Base). In Con, aural temperature (Taural) and the rate of CHO oxidized (CHO..) were not altered from the values at Base during Cooling, whereas the following were increased: the rate of heat production (Hprod, 1.9-fold), thigh electromyographical activity (EMG, -2.5-fold), and the rate of fat oxidized (FAT0., -1.7-fold). In Post-Ex, Taural did not decrease from the value at Base during Cooling, and compared with Con, EMG, CHOOX and the rate of heat loss were not different, whereas Iprod (P 6 0.01), FATOX (P S 0-01) and mean skin temperature (P 6 0.01) were higher, and Taura1 was lower (P 6 0.05). It is concluded that during moderate cold stress, shivering thermogenesis is supported by an increase in the oxidation of fat, and despite an alteration in the initial thermoregulatory responses to Cooling -2 h after exhaustive exercise, thermoregulation was not impaired.

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Section: Physiological Responses To Moderate Cold Stresssupporting

confidence: 41%

Physiological responses to moderate cold stress in man and the influence of prior prolonged exhaustive exercise

Weller¹,

Greenhaff²,

Macdonald³

1998

Experimental Physiology

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“…In contrast to these animal studies, little is known about fuel metabolism in humans. Although it has been reported in humans that cold exposure increased basal levels of plasma FFA, glycerol, catecholamines and that it decreases plasma glucose and insulin (for a review see 14,17), these changes did not reveal any information with respect to substrate utilization. Using the well-known indirect calorimetry and nonprotein respiratory exchange ratio technique, we have recently demonstrated that the cold-induced increase in heat production (fasting semi-nude subjects at rest for 2 h at 10 °C, 1 ms'wind) was associated with a 58% and 63% increase in carbohydrate and lipid oxidation, respectively, and an un- Sl91 -S193, 1992. Recent advances on the influence of cold exposure on energy metabolism in animals and humans are summarized.…”

Section: Human Experimentsmentioning

confidence: 86%

Energy Metabolism During Cold Exposure

Vallerand¹,

Jacobs²

1992

Int J Sports Med

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Recent advances on the influence of cold exposure on energy metabolism in animals and humans are summarized. Although the cold-induced enhancements in carbohydrate metabolism have been the focus of numerous studies, it was only recently that pieces of evidence from animal studies have suggested that cold exposure exerts an insulin-like effect on peripheral tissue glucose uptake, which appears to proceed primarily via insulin-independent pathways. Interestingly, this phenomenon was observed in insulin-sensitive tissues of warm- a well as cold-adapted rats. Whereas previous human studies have concentrated on the cold-induced changes in basal levels of hormones and metabolic substrates, recent work from our laboratory has demonstrated that exposure to cold at rest shifts substrate utilization from mainly lipids at thermal neutrality to carbohydrates, representing the main fuel for shivering thermogenesis. Further investigation has revealed that the marked increment in carbohydrate oxidation in cold-exposed humans is derived from a greater utilization of both circulating glucose and intramuscular glycogen. With respect to lipid metabolism, recent studies have shown that the cold-induced increase in lipid oxidation in man is fuelled primarily by the fatty acids released from white adipose tissue triglycerides (TG) and possibly intramuscular TG, not plasma TG. One practical application of this work on energy metabolism in the cold resides in the pharmacological approach to improve cold tolerance, where pharmacological agents that alter energy metabolism and substrate utilization could be used to enhance cold thermogenesis and produce warmer body temperatures.

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“…Attributing the eects primarily to increased stimulation of CNSmediated function is attractive because combined application of caeine and ephedrine has been demonstrated previously to be synergistic for functions which, in contrast with exercise, are involuntary in nature. Vallerand et al (1989) reported that the metabolic rate was signi®cantly higher in resting shivering subjects after combined caeine and epinephrine treatment than with either caeine or epinephrine alone. Similarly, Astrup et al (1991) reported similar results for average daily energy expenditure over several weeks in a clinical trial of combined caeine and ephedrine used to treat obese individuals.…”

Section: Discussionmentioning

confidence: 97%

Effects of caffeine, ephedrine and their combination on time to exhaustion during high-intensity exercise

Bell¹,

Jacobs²,

Zámečník³

1998

European Journal of Applied Physiology

106

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This study investigated the effects of acute ingestion of caffeine (C), ephedrine (E) and their combination (C+E) on time to exhaustion during high-intensity exercise. Using a repeated-measures, double-blind design, eight male subjects exercised on a cycle ergometer at a power output that led to exhaustion after about 12.6 min during a placebo (P) control trial. They did this 1.5 h after ingesting either C (5 mg x kg[-1]), E (1 mg x kg[-1]), C+E, or P. Trials were separated by 1 week. Venous blood was sampled before and during exercise. The mean (SD) times to exhaustion were 12.6 (3.1) (P), 14.4 (4.1) (C), 15.0 (5.7) (E) and 17.5 (5.8) (C+E) min. Only the C+E treatment significantly increased time to exhaustion compared to P. Oxygen consumption (VO2), carbon dioxide production (VCO2), minute ventilation (VE) and the respiratory exchange ratio (RER) were similar during exercise for all trials. Heart rate during exercise was significantly increased for the C+E and C trials compared to P. Subjective ratings of perceived exertion during exercise were significantly lower after C+E compared to P. All treatments significantly increased lactate levels. Free fatty acid (FFA) levels were significantly increased by C ingestion. Glycerol levels were increased by C+E and C ingestion. Glucose levels were also higher with the drug treatments compared to P. Increased monamine availability after C+E treatment was suggested by measurements of catecholamines and dopamine. In conclusion, the combination of C+E significantly prolonged exercise time to exhaustion compared to P, while neither C nor E treatments alone significantly changed time to exhaustion. The improved performance was attributed to increased central nervous system stimulation.

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Mechanism of enhanced cold tolerance by an ephedrine-caffeine mixture in humans

Cited by 32 publications

References 20 publications

Physiological responses to moderate cold stress in man and the influence of prior prolonged exhaustive exercise

Physiological responses to moderate cold stress in man and the influence of prior prolonged exhaustive exercise

Energy Metabolism During Cold Exposure

Effects of caffeine, ephedrine and their combination on time to exhaustion during high-intensity exercise

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