The modifying effects of 24R,25-dihydroxyvitamin D3 [24R,25(OH)2D3], a vitamin D3 derivative, on glandular stomach carcinogenesis were investigated in male Wistar rats by N-methyl-N′-nitrosoguanidine (MNNG) and sodium chloride exposure during the postinitiation phase. A total of 130 male 6-week-old rats was divided into five groups. Groups 1–3 (consisting of 30 rats/group) were given MNNG in drinking water at a concentration of 100 ppm and were simultaneously fed a diet supplemented with 10% NaCl for 8 weeks. They were fed a diet containing either 5.0 ppm (group 1) or 2.5 ppm (group 2) 24R,25(OH)2D3 or were kept on the basal diet alone (group 3) for the following 57 weeks. Rats in groups 4 and 5 were given 24R,25(OH)2D3, as were animals in groups 1 and 3, but did not receive the MNNG + NaCl treatment. The total incidence of combined atypical hyperplasias and adenocarcinomas in the glandular stomachs was significantly lower in group 1 (24%) than in group 3 (70%; P < 0.01). The mean numbers of atypical hyperplasias or adenocarcinomas of the glandular stomachs in groups 1 (0.31) and 2 (0.66) were also significantly decreased (P < 0.01 and P < 0.05, respectively) as compared to the group 3 value (1.21). Thus, the development of cancerous and precancerous lesions in the glandular stomach was decreased by exposure to 24R,25(OH)2D3 in a dose-dependent manner. Urinary calcium levels were increased by this vitamin D3 derivative (in line with the applied dose) when assayed at 10, 30, and 62 weeks, regardless of the MNNG + NaCl treatment. The present results clearly indicate that 24R,25(OH)2D3 exerts chemopreventive effects, possibly by influencing calcium pharmacodynamics, when given during the postinitiation phase of glandular stomach carcinogenesis in rats.

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Supported by a Grant-in-Aid for Cancer Research from the Ministry of Health and Welfare of Japan.

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