Induced thermal resistance in the mouse ear

Abstract

The mouse ear (pinna) was used to investigate the effect of two hyperthermic treatments. Heating was by immersion in hot water at 43.5 degrees C. A single treatment of about 50 minutes was required to cause necrosis in 50% of the ears heated. When heat treatment was given in two equal fractions the total heating time had to be increased if the interval between fractions was greater than four hours. By 24 hours a total treatment of about 100 minutes was required, indicating almost complete recovery from the first heating. Priming treatments at 43.5 degrees C induced thermal resistance to a second heat treatment at 43.5 degrees C. Maximum resistance was observed one day after a 20 minute priming and two days after a 40 minute priming, when the heating time had to be increased to 120 minutes, an increase by a factor of 2.4. Shorter priming treatments induced less resistance, the minimum heating time to produce an effect being two minutes. In all cases the effect decreased during the next four to five days. These results indicate that the reduced response of tissues to fractionated hyperthermia is due both to the repair of sublethal heat damage and induction of thermal resistance.

Importance of preheating temperature and time for the induction of thermotolerance in a solid tumour in vivo

“…Both the fractionation interval necessary to obtain maximum thermotolerance increased as the preheating time was increased. This agrees with earlier observations on cell cultures in vitro (Gerner et al, 1976;Li et al, 1982;Nielsen & Overgaard, in press, and on different normal tissues in vivo (Law et al, 1979;Hume & Marigold, 1980;Urano et al, 1980;Rice et al, 1982;Field & Anderson, in press). Recently, studies on solid tumours have also shown that at a given interval the degree of thermotolerance increased as the preheating time was increased (Maher et al, 1981;.…”

“…Such a delay period was not observed in the present study. The time for loss of thermotolerance clearly depended on the preheating time as also demonstrated on normal tissues in vivo (Law et al, 1979;Hume & Marigold, 1980 (Figs 7 and 8). A similar relationship has also been demonstrated for cell cultures (Henle et al, 1979;Nielsen & Overgaard, in press).…”

“…However, in these studies the TTRmax and the time required to obtain TTRmax were also linear functions of the logarithm of the relative survival following preheating. Also the data from Law et al (1979) may indicate a linear relationship between the maximum degree of thermotolerance in mouse ears and the duration of the prior heat treatment at 43 5°C, at least after pretreatments up to 20 min.…”

“…Using either a constant preheating time at different temperatures (Hume & Marigold, 1980;Li & Hahn, 1980) or different preheating times at a constant temperature (Gerner et al, 1976;Law et al, 1979;Rice et al, 1982), these studies suggest that the higher the degree of damage induced by preheating, the larger the induced thermotolerance, and the later the maximum tolerance is expressed. However, from these studies it is not clear whether it is the level of heat damage after preheating or the preheating temperature itself which is most important for thermotolerance.…”

Thermal radiosensitization in Chinese hamster (V79) and mouse C3H 10T 1/2 cells. The thermotolerance effect

“…Further results of Miyakoshi et al (1979) showed that radiosensitization was diminished if low temperature hyperthermia (42.0°C) preceded high temperature hyperthermia at 45.0°C causing thermotolerance. Results from normal tissue studies in vivo also show that a conditioning heat treatment given at various times before subsequent heating and irradiation could result in thermal tolerance and reduced TERs (Henle 1982, Law et al, 1979a,b, Dethlefsen and Dewey 1982. In these studies it was shown that the reduction in TERs was not temporally related to the onset of thermal tolerance (Marigold and Hume, 1982;Law et al, 1979a,b).…”