MacNaughton K W, Sathasivam P, Vallerand A L, Graham T E
School of Human Biology, University of Guelph, Ontario, Canada.
J Appl Physiol (1985). 1990 May;68(5):1889-95. doi: 10.1152/jappl.1990.68.5.1889.
Cold stress and caffeine ingestion are each reported to increase plasma catecholamines, free fatty acid (FFA) concentrations, and energy metabolism. This study examined the possible interaction of these two metabolic challenges in four double-blind counterbalanced trials. Young adult men (n = 6) ingested caffeine (5 mg/kg) or placebo (dextrose, 5 mg/kg) and rested for 2 h in 28 or 5 degrees C air. Cold stress alone elevated (P less than 0.05) plasma norepinephrine, metabolism (O2 consumption, VO2), and respiratory exchange ratio (RER). Caffeine alone increased (P less than 0.05) plasma epinephrine and FFA but not RER. When the two challenges were combined (caffeine plus 5 degrees C for 2 h) norepinephrine and epinephrine were increased (P less than 0.05) as was FFA. However, VO2, RER, and skin and rectal temperatures were not different from the responses observed at 5 degrees C after placebo ingestion. The data suggest that caffeine selectively increases plasma epinephrine, whereas cold air increases norepinephrine. During the cold exposure, increasing epinephrine and FFA above normal levels did not appear to influence the metabolic or thermal responses to the cold stress. In fact the increase in RER suggested a greater carbohydrate oxidation.
据报道，冷应激和摄入咖啡因均可增加血浆儿茶酚胺、游离脂肪酸（FFA）浓度及能量代谢。本研究在四项双盲平衡试验中检测了这两种代谢应激因素之间可能存在的相互作用。年轻成年男性（n = 6）摄入咖啡因（5 mg/kg）或安慰剂（葡萄糖，5 mg/kg），并分别在28℃或5℃的空气中静息2小时。单独冷应激会使血浆去甲肾上腺素、代谢（耗氧量，VO₂）及呼吸交换率（RER）升高（P < 0.05）。单独摄入咖啡因会使血浆肾上腺素和FFA增加（P < 0.05），但不会使RER升高。当两种应激因素同时存在时（咖啡因加5℃持续2小时），去甲肾上腺素、肾上腺素及FFA均会增加（P < 0.05）。然而，VO₂、RER以及皮肤和直肠温度与摄入安慰剂后在5℃时观察到的反应并无差异。数据表明，咖啡因可选择性增加血浆肾上腺素，而冷空气会增加去甲肾上腺素。在冷暴露期间，将肾上腺素和FFA增加至正常水平以上似乎并未影响对冷应激的代谢或热反应。事实上，RER的增加表明碳水化合物氧化增加。
