Misonidazole-induced radio-resistance in normal and preirradiated jejunal mucosa

Radiosensitivity of jejunal mucosa after whole abdomen irradiation and CDDP pretreatment

Pretreatment of mice with a single radiation dose of 11.5 Gy or with fractionated irradiation (2 x 6.5 or 7.5 Gy, with an interval time of 12 hr) led to a relative decrease in the radiosensitivity of jejunal crypt cells when a second single dose of radiation was delivered 2 months later. When the same irradiation pretreatment was combined with CDDP (6 mg/kg, i.p.) injected 12 hr after single radiation or between two equal doses of radiation, similar crypt cells resistance was obtained. The combination of CDDP with irradiation did not modify the radiosensitivity of jejunal crypts in comparison with irradiation alone, even when the total radiation dose was delivered in 2 split doses. This induced radioresistance was demonstrated to be a reflection of late injury on intestinal tissue, presumably due to hypoxia resulting from vascular damage. It seems that the administration of CDDP did not change the possible hypoxia suspected in crypt cells of mice pretreated with single radiation dose. However, mouse lethality increased significantly when CDDP was combined with irradiation.