暑熱順化ウサギの体温調節能変化に関する研究
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暑熱環境への長期暴露により生体の体温調節反応がいかに変化するのかを知るために,体重2.5kgから2.8kgの雄性成熟ウサギを用いて実験を行なった.まず,室温30.0℃・相対湿度60%の暑熱環境下で24週間飼育した暑熱順化ウサギと,室温25.0℃・相対湿度60%の中性温域で同期間飼育した対照ウサギの両群に,頚部のみの軽固定下にて,10.0℃から40.0℃の温度帯の温熱負荷を全身に加え,その間に深部体温の指標としての直腸温,耳介皮膚血管運動の指標としての耳介皮膚温等を測定した.その結果,暑熱順化ウサギの直腸温の変動幅は,1.1±0.6℃ (Mean±S.D.)で,対照ウサギの1.6±0.3℃に比べ有意に小さくなった.更に,暑熱負荷による耳介皮膚血管拡張,及び寒冷負荷による耳介皮膚血管縮小誘発の閾値温は,各々27.5±1.2℃,21.8±3.3℃と対照ウサギのそれら(<25.0℃,14.7±2.9℃)に比べ,高温側へシフトしていた.しかしこの両群における差異は,Sodium Pentobarbital(20mg/kg, i.p.)による全身麻酔下では消失した.この結果から.連続的な暑熱暴露によりウサギは,1)末梢の温熱刺激に対する感受性が増大する事により,2)温熱負荷時の深部温の変動幅が減少する事,3)この反応の修飾には神経機構が関与している可能性がある事が示唆された.さらに,同一環境温下において,両群にadrenalineのα-blockerの一つであるphetolamine mesylate(3mg/kg, i.v.)を投与した時の耳介皮膚血管拡張の程度が異なる事から,耳介皮膚に於ける交感神経vaso-constrictorのtoneは,両群で異なるものと思われる.In order to clarify the functional modifications which appeared during heat acclimation, male albino rabbits weighing from 2.5kg to 2.8kg were continuously exposed to a warmer environment (ambient air temperature (Ta)=30.0℃, relative humidity (r. h.)=60%) for 24 weeks (Heat-Acclimated). And, various parameters to general thermal stimulation were compared with those in control rabbits (Control) which were reared in thermoneutral environment (Ta=25.0℃, r. h.=60%) for same duration. For the general thermal stimulation, rabbits were lightly restrained only around the cervical region under the conscious condition. The changing rate of Ta was set to be 0.5℃/min. Pattern changes in rectal temperature (Tre) during Ta displacement was 1.1±0.2℃ (Mean±S. D.) in Heat-Acclimated. and 1.6±0.3℃ in Control, respectively. Mean threshold temperature of Ta at the beginning of vasodilation of the ear skin was 27.5±1.2℃ in Heat-Acclimated, but in Control, vasodilation already occurred under the thermoneutral condition in 25.0℃ of Ta. On the other hand, vasoconstriction of the ear skin in Heat-Acclimated occurred at 21.8±3.3℃ of Ta, about 7.0℃ higher than that of Control (14.7±2.9℃). It is supposed that during heat acclimation, shift of threshold temperature of Ta for inducing peripheral vaso-dilation and-constriction appeared, resulting in prevention of the change of core temperature. Under anesthesia with sodium pentobarbital (20mg/kg, i. p.), however, differences in pattern changes of the parameters between two groups disappeared. These differences during Ta displacement could be observed again two or three days after anesthesia. From these results, it is assumed that functional modifications during heat acclimation might occur in the neuronal mechanisms which were influenced by anesthesia. In order to know what is important for these differences, vasomotor responses in the ear to intravenous administration of α adrenergic-biocker (phentolamine mesylate, 3 mg/kg, i. v.) were observed and these sympathetic vasoconstrictor tones were compared. Before intravenous administration of phentolamine, Tea at 25.0℃ was maintained at near the Ta both in Control and Heat-Acclimated. After administration of the drug, however, the degree of vasodilation in the ear skin was larger in Control than in Heat-Acclimated. From this result, it is suggested that at the same Ta, vaso-constnctor tone is different between Heat-Acclimated and Control.
- 1986-12-27
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