Ingesting a combination of caffeine and ephedrine (C+E) has been shown to raise metabolic heat production and body temperature. This side effect of C+E ingestion may be positive during a cold stress scenario, however, during heat stress it could prove to be detrimental. Thus, the purpose of this study was to clarify the effect of C+E ingestion on body temperature regulation during moderate exercise in a hot dry environment.
Ten, healthy, non heat acclimated, males exercised at 50% VO2peak in a 40 degrees C and 30% RH environment until rectal temperature reached 39.3 degrees C; heart rate (HR) remained at 95% of peak value or greater for 3 min, dizziness or nausea precluded further exercise, or 3 h had elapsed. They did this four times at weekly intervals: familiarization (Fam), control (Cont), placebo, and C+E (5 mg . kg(-1) caffeine + 1 mg . kg(-1) ephedrine) trials. The Fam and Cont treatments were done first and sequentially while the placebo and C+E treatments were balanced and double-blind. Tolerance times, mean skin temperature (Tsk), rectal temperature (Tre), Vo2, Vco2, VE, sweat rate (SR), HR, and sensation of thermal comfort were measured.
Tolerance times (mean+/-SD in minutes) were similar for the placebo (120.0+/-28.4) and C+E (121.3+/-33.9) trials and both times were significantly longer than Cont (106.6+/-24.0) trial. C+E did not affect Tsk, initial TrC, delta Tre, SR or the sensation of thermal comfort. VO2 and VF, were significantly increased by C+E. HR was elevated by C+E compared with the other trials, but only during the initial 20 min of exercise.
Although the metabolic rate was slightly increased with C+E treatment, it was sufficiently offset by increased heat loss mechanisms so that internal body temperature was not increased during moderate exercise in a hot, dry environment.
"They were 21 males (age: 19.7 ± 0.4 00 yrs, mean ± SD; height: 165 ± 1.5 cm; body mass: 55.1 ± 1.1 kg) and 19 females (age: 19.7 ± 0.2 yrs; height: 155.6 ± 1.7 cm; body mass: 45.6 ± 1.3 kg). All of them were free from taking drugs or medications, and the females were in the same phase of their menstrual cycles (follicular phase) to avoid any effects of reproductive hormones on body temperature (Bell et al., 1999). All experimental procedures were fully explained to them before the experiments and their informed consent was given. "
[Show abstract][Hide abstract] ABSTRACT: Thermally comfortable zones in Vietnamese were investigated during winter in Hanoi. The subjects were 21 males (age: 19.7 +/- 0.4 yrs; height: 165 +/- 1.5 cm; body mass: 55.1 +/- 1.1 kg) and 19 females (age: 19.7 +/- 0.4 yrs; height; 155.6 +/- 1.7 cm; body mass: 45.6 +/- 1.3 kg). Each participant entered singly the climatic chamber controlled at 22 degrees C and 40% RH. After 20 min rest, the participant was requested to indicate on a 7-point scale (Table 1) how he or she felt to the room temperature given. Then, the room temperature increased by 1 degrees C over 10 min every 20 min. Just before the rise of the room temperature, the participant judged his or her thermal sensation. More than 90% of the participants felt 24-29 degrees C of the room temperature as "slightly cool", "neutral" and "slightly warm" (Table 2). We defined these sensations as "thermally comfort". These thermally comfortable zones were quite higher than those (20-24 degrees C) recommended by ISO-7730 (1994). We discussed these discrepancies in terms of higher establishment of thermoregulatory set-point in the Vietnamese.
[Show abstract][Hide abstract] ABSTRACT: l-Ephedrine is an active ingredient in several herbal formulations with a mechanism of action similar to amphetamine and methamphetamine. However, its potential to damage dopaminergic terminals in the caudate/putamen (CPu) has yet to be fully evaluated. The studies here used in vivo brain microdialysis experiments to determine the systemic doses and extracellular brain levels of l-ephedrine necessary to produce similar increases in CPu extracellular dopamine and marked hyperthermia that were previously shown necessary for amphetamine-induced neurotoxicity in male Sprague-Dawley rats. At an environmental temperature of 23 degrees C, a single 40 mg/kg intraperitoneal (ip) dose of l-ephedrine produced marked hyperthermia (>/= 40 degrees C), peak microdialysate ephedrine levels of 7.3 +/- 1.2 microM, and a 20-fold increase in microdialysate dopamine levels. Twenty-five mg/kg produced a lesser degree of hyperthermia, peak microdialysate ephedrine levels of 2.6 +/- 0.4 microM, and a 10-fold increase in dopamine levels. Three doses of 40 mg/kg given at 3-h intervals or 4 doses of 25 mg/kg l-ephedrine given at 2-h intervals were compared with 4 doses of 5 mg/kg d-amphetamine given at 2-h intervals. Multiple doses of either ephedrine or amphetamine caused severe hyperthermia (>/= 41.3 degrees C) but striatal tissue levels of dopamine 7 days after dosing were reduced only 25% or less by ephedrine compared to the 75% reductions produced by amphetamine. The increases in CPu microdialysate levels of serotonin produced by either 4 x 25 mg/kg l-ephedrine or 4 x 5 mg/kg d-amphetamine did not significantly differ, but elevation of dopamine levels by d-amphetamine were over 2-fold times the level caused by l-ephedrine. Microdialysate glutamate levels were elevated to the same extent by either 25 mg/kg l-ephedrine or 4 x 5 mg/kg d-amphetamine. l-Ephedrine may not be as neurotoxic to dopaminergic terminals as d-amphetamine, because non-lethal doses of l-ephedrine do not sufficiently increase the CPu dopamine levels within nerve terminals or the extracellular space to those necessary for a more pronounced long-term dopamine depletion.
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