The X-ray induction of tumors was examined in five-week-old male Otsuka Long-Evans Tokushima Fatty (OLETF) rats, treated with two 10 Gy doses to the gastric region with a 3-day interval (total 20 Gy). After irradiation, the rats received the commercial diet MF and tap water and were maintained for up to 564 days. The mean serum glucose level in the X-irradiated group was significantly lower than that in the non-irradiated animals at the 18 month time point. The total tumor incidence was 27/30 (87.1%) in the treated rats (islet tumors, gastric tumors, sarcomas, seminomas, adrenal tumors, kidney tumors, papilloma, lymphomas and mammary tumors). Islet tumors, generally showed to be positive for insulin by immunohistochemistry, developed in 19 rats (63.3%), and were associated with low serum glucose. Since spontaneous tumors observed in 6/19 (31.6%) rats (sarcomas, kidney tumors, duodenum tumors, seminoma, adrenal tumor and squamous cell carcinoma) did not include any insulinomas, these are clearly induced by X-irradiation in OLETF rats.

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