Urano M, Kahn J
Radiat Res. 1983 May;94(2):350-8.
Cultured cells can be sensitized to low-temperature hyperthermia (below 43.0 degrees C) by a prior heat shock at a high temperature (above 43.0 degrees C) if the heat above 43.0 degrees C is immediately followed by the heat below 43.0 degrees C. This effect has been termed step-down heating (SDH). We have studied the effect of SDH on the response of murine tumor and normal tissues treated at 45.5 degrees C. Animal tumors were eighth-generation isotransplants of a spontaneous fibrosarcoma in C3Hf/Sed. mice. Tumor response was studied by TG (tumor growth) time assay, i.e., determination of the time required for half the treated tumors to reach 1000 mm3 from the first day of treatment. Normal tissue response was studied in the mouse foot. End point was the time to induction of a score 4.0 (loss of a toe) or greater reaction in half the treated animals, RD50. The SDH at 41.0 degrees C sensitized the response of tumor and normal tissues to 45.5 degrees C. The enhancement ratios were congruent to 1.7 for both tissues, indicating no differential sensitization between tumor and normal tissues. No sensitization was observed if the SDH was given immediately after a second dose of 45.5 degrees C given 6 hr to 5 days following the first dose of 10 min at 45.5 degrees C. The SDH appeared not to inhibit the development of thermal resistance as evidenced by no appreciable changes in the thermal resistance ratio.
如果在43.0℃以上的高温热休克后紧接着进行43.0℃以下的低温热疗（低于43.0℃），培养的细胞可以对低温热疗产生敏化作用。这种效应被称为逐步降温加热（SDH）。我们研究了SDH对在45.5℃处理的小鼠肿瘤和正常组织反应的影响。动物肿瘤是C3Hf/Sed小鼠自发纤维肉瘤的第八代同基因移植瘤。通过TG（肿瘤生长）时间测定法研究肿瘤反应，即测定从治疗第一天起，半数治疗肿瘤达到1000mm³所需的时间。在小鼠足部研究正常组织反应。终点是半数治疗动物诱导出4.0分（趾头缺失）或更严重反应的时间，即RD50。41.0℃的SDH使肿瘤和正常组织对45.5℃的反应敏感化。两种组织的增强比均为1.7，表明肿瘤组织和正常组织之间没有差异敏化。如果在第一次45.5℃ 10分钟剂量给药后6小时至5天给予第二次45.5℃剂量后立即给予SDH，则未观察到敏化作用。SDH似乎不会抑制热耐受性的发展，热耐受比没有明显变化证明了这一点。
