Abstract

• Induction of intestinal tumor by subcutaneous injection of 1, 2-dimethylhydrazine(DMH), 20 mg/kg/week, during 20 weeks was studied in rats fed by vitamin A(retinol) 50 µg, 500 µg/day.
  Mucosal epithelial cell hyperplasia and mitosis in one crypt was not significantly inhibited by vitamin A administration(P>0.05). In electron microscopic findings, the cytoplasmic vacuoles were decreased in DMH+vitamin A-treated rats than DMH only. Dysplasia of the colonic mucosa in DMH+vitamin A-treated group were more slowly developed than DMH-treated rats. In DMH-treated rats the tumors were early detected after 14 weeks, but in DMH+vitamin A-treated groups were seen after 20 weeks.
  All these findings suggest that vitamin A can effectively prevent cytotoxicity of carcinogen in early phase, but can not prevent carcinogenesis in late phase.