ナキウサギ(Pika, Whistle Rabbit)の発熱反応
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概要
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ナキウサギ(pika)の体温が家ウサギより高い理由は,その高い熱産生能と低い熱放散能に起因するが,運動量・耳介の含む体表面積や行動性体温調節能などを統合して考えるべきである.ナキウサギは麻酔剤に高感受性を示す反面,腹腔内投与の外因性発熱物質(LPS-pyrogen)に反応しないと報告されている.今回,私共は細い耳介静脈注入の困難を克服して,22℃室内に飼育のナキウサギ(n=9,平均体重:262.2g)を人工気象室(28℃,60% rh)に移し3.8μg/kgのLPS-pyrogenを耳介静脈注入して発熱反応の有無を検索し,次の結果を得た.(1)無麻酔,無拘束のナキウサギの平均直腸温(39.34℃)はLPS-pyrogen静注後,20分の潜時を経て上昇開始,最高直腸温40.23℃(ΔTre:0.73℃)を経て発熱持続時間70分の一峰性発熱曲線を示した.(2)呼吸頻度(RR)はLPS静注前値108c/min,発熱極期100c/min,発熱終了時92c/minと変化し,これは家ウサギのRR変化率より小さく,熱放散反応の不備を示唆している.(3)発熱上昇期にはふるえ(shivering)熟産生,立毛反射や体動減少など,熱産生反応や熱保存反応には首尾一貫性がみられ,この結果からナキウサギが家ウサギに劣らない体温上昇能のみならずLPS-pyrogenによる発熱特性を有することが明らかになった.Pikas's better heat conservation ability thought to be due to its higher metabolic rate, poor heat dissipation through weak panting and smaller ear surface area. Although it's very sensitive to narcotics, it responds poorly to mtrapentoneal Lipopolysaccharide (LPS) pyrogen. In this experiment 9 pikas (mean body weight: 262.2g) reared at 22℃ were subjected to intravenous LPS pyrogen (3.8ug/kg) in the environmental control chamber (temp 28℃ and 60% r. h.). Throughout the experiment the animals were unrestrained in cages with thermister probe in situ deep in rectum and fixed to the tail by adhesive plaster. 15 minutes prior to i. v. pyrogen injection, rectal temperature (Tre) and respiratory rate (RR) were recorded every 5 minutes, and thereafter every 10 minutes. The LPS pyrogen evoked a monophasic fever (mean peak Tre: 40.23℃, mean ΔTre: 0.73℃±0.3℃) which persisted for 70 minutes after a mean latent period of 20 minutes. RR decreased from precontrol rate of 108c/min to 100c/min at the peak of fever to a low 92c/min at the end of the pyrexia. It was also observed that the pika developed piloerection and shivering during the rising phase of the fever. Occasionally they hcked their body but mostly they had minimal movement during the pyrexic period. These observation show that Pika rabbits can elicit fever with i. v. LPS pyrogen but the heat loss mechanisms differ from those of albino rabbits.
- 1987-09-30
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