• duodenal crypt;
  • mitotic rhythm;
  • carcinomas;
  • stem cells

The presence of a tumor generally changes the mitotic activity of the normal cell population in mice. In the present work, the mitotic activity of the duodenal crypt enterocytes in EA21a mammary carcinoma-bearing mice was determined. The results show that there is a patent circadian variation in normal mice and, in the presence of the EA21a mammary tumor, cell proliferation is stimulated. Stimulation was evident in enterocytes from the intermediate as well as the superficial regions of the crypt. Some humoral factors produced by the transplanted tumor could interfere with the regulatory mechanism of the mitotic activity of duodenal crypt enterocytes.