Effect of Change in Environmental Air Temperature on Heart Rate in Thermally Acclimated Rats

1.暑熱(30℃, 60% r. h.)又は寒冷(10℃, 60% r. h.)環境で4週間以上飼育したWistar系の雄ラットを使用した.無麻酔-半拘束状態で環境温を20℃から30℃の範囲で10℃/30minの温度変化速度で往復変化させた.2.暑熱順化群,寒冷順化群のいずれのラットも心拍数は環境温の上昇に伴い減少し,環境温の低下に伴い増加した.心拍数と環境温は有意の負の相関を示し,その回帰直線の勾配(beats/min・℃)の平均値(M.±S. E.)は暑熱順化群で-10.8±1.5 (n=6),寒冷順化群で-5.2±1.0 (n=6)の結果をえた.3.sodium pentobarbital麻酔下における同様な実験では,心拍数と環境温の負の相関は著しく減弱するか消失した.心拍は直腸温と正の相関を示した.4.以上の事実から無麻酔-半拘束状態で環境温を変化させた場合の心拍数の変化は,皮膚温度受容により誘起される循環反射と考えられ,温度順化は,この反射を修飾したものと結論される.Adult male Wistar rats were thermally acclimated at 30℃ and 10℃ for more than 4 weeks with ad libitum food and water. During the experiment, conscious animals were kept in a small cage (5cm×10cm×22cm) individually. Environmental air temperature was changed from 20℃ to 30℃ at 1℃/3min, and vice versa. Temperatures of environmental air and rectum were detected by means of thermocouples of copper and constantan. Heart rate was counted continuously from electrocardiogram. An increase in heart rate was observed during a fall of environmental air temperature, while a decrease in heart rate was observed during a rise of environmental air temperature. When values of heart rate were plotted against environmental air temperature, slopes of the regression line were -10.8±1.5 (n=6) and -5.2±1.0 (n=6) (beats/min・℃, Mean±S. E.) in heat-and cold-acclimated rats, respectively. These relationship vanished in rats anesthetized with sodium pentobarbital (50mg/kg, i. p. and 13mg/hr., i. v.), while heart rate increased with an increase of rectal temperature. From these results, it is suggested that these vasomotor responses to changes in environmental air temperature in this range seem to be a reflex action triggered by the cutaneous thermoreception, which are affected in the process of thermal acclimation