Shido O, Sakurada S, Hashimoto T, Fujikake K, Nagasaka T
Department of Physiology, School of Medicine, Kanazawa University, Japan.
Can J Physiol Pharmacol. 1993 Dec;71(12):904-9. doi: 10.1139/y93-137.
The present study was conducted to investigate day-night variations of plasma thyroid hormone and energy substrate levels in rats after acclimation to heat loaded for several hours at a fixed time per day. The heat-acclimated rats were exposed to an ambient temperature of 33 degrees C for 5 h in the last half of the dark phase for 16 consecutive days, while the control rats were kept at 24 degrees C for the same period. After completing the schedule, plasma levels of triiodothyronine (T3), free T3 (FT3), thyroxine (T4), free T4 (FT4), cortisol, triglyceride, nonesterified fatty acid, total protein, and glucose were measured at 3-h intervals between 00:00 and 18:00 (dark phase, 03:00-15:00). The plasma levels of T3 and FT3 of the heat-acclimated rats were higher than those of the controls in the last half of the dark phase. Similar differences were observed for T4 and FT4 levels. The plasma cortisol level was consistently higher in the heat-acclimated rats than in the control rats. There were no particular differences in energy-substrate levels between the two groups at any time of the day. These results indicate that heat exposure at a fixed time per day alters the pattern of day-night variations of plasma thyroid hormone levels in rats. It is noteworthy that the plasma levels of thyroid hormones, especially T3 and FT3, increased during the period when the rats had been previously exposed to heat.
本研究旨在探讨大鼠在每天固定时间接受数小时热负荷适应后，血浆甲状腺激素和能量底物水平的昼夜变化。连续16天，在暗期的后半段将热适应大鼠暴露于33℃的环境温度下5小时，而同期对照大鼠饲养在24℃环境中。完成该实验安排后，在00:00至18:00（暗期为03:00 - 15:00）期间每隔3小时测量一次血浆三碘甲状腺原氨酸（T3）、游离T3（FT3）、甲状腺素（T4）、游离T4（FT4）、皮质醇、甘油三酯、非酯化脂肪酸、总蛋白和葡萄糖的水平。热适应大鼠的血浆T3和FT3水平在暗期后半段高于对照组。T4和FT4水平也观察到类似差异。热适应大鼠的血浆皮质醇水平始终高于对照大鼠。两组在一天中的任何时间能量底物水平均无明显差异。这些结果表明，每天固定时间的热暴露改变了大鼠血浆甲状腺激素水平的昼夜变化模式。值得注意的是，在大鼠先前暴露于热的时间段内，甲状腺激素的血浆水平，尤其是T3和FT3升高。
