Effect of prolonged heating on the thermal enhancement ratio in X-irradiated murine intestine.

When the jejunum in mice was heated for 20-180 min at temperatures between 40.3 and 42.3 degrees C, followed immediately by X-irradiation, the thermal enhancement ratio (TER) for crypt survival increased and then tended to decline with longer heating times. At the higher temperatures, the TER was higher and the peak value was reached with shorter heating times. The decline in TER with longer heating times may be due to the development of thermotolerance.