The response of the rat tail to hyperthermia.

When the cartilage of the tail of a baby rat is exposed to temperatures between 41 degrees C and 46 degrees C either necrosis or a small degree of stunting in growth may occur. Isoeffect curves relating time and temperature for both these endpoints for normal and clamped tissue were found to be parallel, a doubling of heating time or an increase in temperature of 1 degree C having the same effect in all cases. Clamping sensitizes the tails by a factor of about three in heating time, equivalent to a temperature difference of 1.5 degrees C. Arrhenius plots show an inactivation energy of 140 kcal/mole. This is similar to that found by other workers using different endpoints, and supports the suggestion that protein denaturation is a critical target for direct heat damage.