ACUTE AND PROTRACTED RADIATION EFFECTS ON SMALL-INTESTINAL MORPHOLOGICAL PARAMETERS

Purpose: To compare the responses of small intestinal morphological pa rameters after acute and protracted doses of radiation. Materials and methods: Male C57BL6 mice were examined 6, 24 and 72 h after whole bod y gamma-irradiation, given either as an acute 5 Gy dose, or as a protr acted (continuous) dose of 20 cGy per day for 25 days to a total dose of 5 Gy. Many different structural parameters at both the light micros copical and ultrastructural levels were assessed quantitatively. Resul ts: At different time points following both schedules there were chang es in the number of villous enterocytes, goblet cells, lamina propria cells and mitotic figures. Ultrastructural changes occurred in the epi thelium. Many of the parameters that showed changes following the prot racted schedule appeared to be returning to normal within 3 days of th e cessation of radiation, a finding which was in contrast with the acu te dose. The protracted schedule produced increases in the number of P aneth cells and in the length of enterocyte microvilli. Conclusions: M any of the responses that occurred after the protracted schedule sugge st that adaptive mechanisms may be being triggered following persisten t exposure to radiation.