Talan M I, Tatelman H M, Engel B T
Laboratory of Behavioral Sciences, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224.
Physiol Behav. 1991 Sep;50(3):613-6. doi: 10.1016/0031-9384(91)90554-2.
Nine-month-old male C57BL/6J mice were subjected to three-hour cold stress tests (partial restraint at 6 degrees C) at 9:00 a.m. or at 1:00 p.m. Tests were repeated three times at two-week intervals at the same time of day. Body temperature was measured by colonic thermoprobe, and metabolic heat production was measured by indirect calorimetry during each test. All mice showed habituation to repeated cold exposures (an improvement of cold tolerance across tests) due to an increase in metabolic heat production. The levels of metabolic heat production were similar during morning and afternoon testing; however, mice tested in the afternoon had consistently poorer cold tolerance, which indicated increased heat loss. Increased heat loss in mice of similar body weight and presumably similar body composition, suggests that there is less effective cold-induced skin vasoconstriction during the afternoon. We hypothesize that the compromised skin vasomotor response during the afternoon cold exposure results from competing effects of vasodilation due to local autoregulation stimulated by a circadian reduction of cardiac output during the sleep phase, and vasoconstriction due to the cold stress.
9个月大的雄性C57BL/6J小鼠于上午9点或下午1点接受3小时冷应激试验（在6摄氏度下部分限制活动）。试验在一天中的同一时间每隔两周重复进行3次。每次试验期间，通过结肠温度探头测量体温，通过间接量热法测量代谢产热。由于代谢产热增加，所有小鼠对反复冷暴露均表现出适应性（跨试验的耐寒性提高）。上午和下午测试期间的代谢产热水平相似；然而，下午进行测试的小鼠耐寒性始终较差，这表明热量损失增加。体重相似且推测身体组成相似的小鼠热量损失增加，表明下午冷诱导的皮肤血管收缩效果较差。我们假设，下午冷暴露期间皮肤血管运动反应受损是由于睡眠阶段心输出量昼夜节律性降低刺激局部自动调节导致的血管舒张与冷应激导致的血管收缩的竞争效应所致。
