Morphological investigations on the small intestinal mucosa of mouse after mild hyperthermic treatment.

Local hyperthermia, when applied as a therapeutic agent against radio-resistant tumours, can result in serious side effects in adjacent non-tumorous tissue, one especially thermo-sensitive organ being the small intestine. An experimental morphological study was therefore undertaken with mice to investigate whether "mild hyperthermia" (41 degrees C for 15, 30 and 60 min) causes alterations at the mucosa of the small intestine, and if so what are these effects and their likely pathomechanisms. Descriptive light and electron microscopical studies and morphometric evaluations are reported on the jejunal mucosa. The observed changes were most extensive after 60 min of 41 degrees C hyperthermia; but even 30 and 15 min hyperthermic treatment was followed by severe degenerative changes. The epithelium of the basal crypts and the stromal cells seemed to remain morphologically unaffected under these conditions, though the stroma can react with a temporary contraction. No "prime event" in the hyperthermia provoked tissue changes can be deducted from the combined light, electron microscopical, and morphometric studies. Comparing, however, the extent of the effects after mild hyperthermia of 60, 30 and 15 min, respectively, four phases of intestinal alterations due to mild hyperthermia and a likely pathomechanism of this treatment can be defined. The clinical implications of the findings are discussed.