Evidence against a systemic humoral factor controlling the intestinal compensatory response following X-irradiation

The investigation was devised to determine whether changes noted in the unirradiated duodenum and colon of single rats after X-irradiation of only the exteriorized rat jejunum and ileum are mediated by a systemic humoral factor. Littermate Holtzman male rats were joined in parabiosis and one month later, the temporarily exteriorized jejunum and ileum of one member was exposed to 1,000 R of 250 kVp X-irradiation. Two days after X-irradiation, and 1, 12 and 24 h after 1 μCi/g body weight tritiated thymidine (6 Ci/mMi) was injected intraperitoneally, rats were sacrificed and appropriate tissues removed. Single rats which had the exteriorized jejunum and ileum irradiated were studied from 1-3 days after irradiation. At autopsy, samples of colon and duodenum were taken for determination of dpm/crypt and dpm/mg of intestine. Crypt cell migration rates were determined employing autoradiography. Tritium content and columnar cell migration rate in duodenum and colon of unirradiated rats compared to irradiated rats indicated that irradiation of one member of the pair had no effect on tritium incorporation or epithelial cell migration in the duodenum or colon of the unirradiated partner. Epithelial cell proliferation and crypt cell migration were increased in unirradiated duodenum and colon of single intestine-irradiated rats. Essentially the same changes were seen in the irradiated member of a parabiotic pair, but none of these changes were noted in the unirradiated member. The absence of stimulation in the unirradiated parabiont suggests that either a systemic humoral factor is not present after X-irradiation or is not present in sufficient concentration to be detected by these methods.