Duodenal crypt survival and crypt cellular recovery kinetics following combined treatment with adriamycin and x irradiation

The appropriate assay time for duodenal crypt-cell survival following whole-body x irradiation and adriamycin treatment of C3H mice was evaluated by estimating the x-irradiation D0 and the 10-clone dose (i.e., the single dose required to lower survival to 10 crypt cells per circumference) at either 1.5, 2.5, or 3.5 days after the last treatment. Also, the mice were injected with 20 μCi of [3H]thymidine either 1 hr prior to initiating the combined treatments or 1 hr before being killed, and a detailed autoradiographic analysis of the surviving crypts was done. The data indicate that 3.5 days after the last treatment is a reasonable time of assay for studies involving x iradiation only or adriamycin plus x irradiation, when the adriamycin was injected either 12 or 48 hr before the x irradiation. However, the more appropriate assay time is also x-ray dose dependent. At 3.5 days, the crypts are in a state of either complete recovery or hyperproliferation following low radiation doses (less than or equal to 900 rad), but at higher doses they are in a state of active regeneration. Thus the mice actually should be evaluated for an appropriate assay time after each specific dose of radiation. Also, the data suggest that (a) the surviving crypts are repopulated with cells which are descendants of slowly proliferating cells at the bottom of the crypts, and (b) the surviving crypts following higher x-ray doses (i.e., > 900 rad; the exponential portion of the survival curve) may not be repopulated from a single surviving crypt cell. The former suggestion is consistent with several previous reports which also suggested that these particular cells are the apparent functional stem cells of the intestinal crypts