Pyrimidine biosynthetic enzymes in rat intestine after small bowel resection.

After small bowel resection in the rat, mucosal hyperplasia and an increase in nucleic acid synthesis and cell proliferation occur in remaining small intestine. Male Sprague-Dawley rate underwent resection of 50 cm of proximal or distal intestine or sham operation. One month and 6 months after surgery, aspartate transcarbamylase, dihydroorotase, and uridine kinase were assayed in whole mucosa, and in some instances, in crypt mucosa ffrom the remaining intestinal segment. In control bowel, enzyme activity was significantly greater proximal compared with distal segments. One month after proximal or distal resection, mucosal enzyme activity per cm of gut was greater in the remnant bowel compared with controls. There was no such difference at 6 months. Specific enzyme activity of whole mucosa did not increase after resection because the assay was influenced by the disproportionately large contribution of villous protein. Specific enzyme activity (including thymidine kinase) of isolated crypt mucosa was significantly increased 1 month after distal resection. In addition, [3H]thymidine uptake into DNA of crypt mucosa from proximal remnants was also significantly increased. These results indicate that after small bowel resection, the enzymes of pryimidine biosynthesis increase in remaining bowel and parallel the accelerated rate of cell proliferation.