Increased hyperthermal response of previously irradiated mouse intestine.

The effect of prior irradiation (6-10 Gy of X rays) on the response of mouse jejunum to 43.0 degrees C hyperthermia was investigated. A dose of 6 Gy has no significant effect on the crypt loss measured after hyperthermia. However, intestine which had received 8-10 Gy showed increased susceptibility to subsequent thermal injury. Between approximately one and 2 weeks after 9 Gy, the thermal response of the intestine of CFLP mice increased such that, at maximal effect, heating pre-irradiated intestine at 43.0 degrees C was approximately equivalent to heating untreated intestine at 43.5 degrees C. The effect of prior irradiation was transient and appeared to have been "forgotten" after 2-3 months, a finding of particular relevance to the clinical situation. The results are discussed with reference to any radiation injury to intestine which might influence the expression of hyperthermal damage in situ.