Effects of prostaglandins on ornithine decarboxylase activity in rat small intestine

Role of prostaglandins on feeding-associated induction of ornithine decarboxylase in small intestine was studied. Rats received intraperitoneal injection of either saline, or 16,16-dimethyl prostaglandin E2, or TRY-200 (a stable prostaglandin I2 analog), or refeeding, after a 44 hr-fast. Four hours later, mucosae from duodenum, jejunum, and ileum were scraped for subsequent measurements of enzyme activity of ornithine decarboxylase by a radiometric technique. Refeeding resulted in a profound induction of enzyme activity throughout the small intestine. Parenteral administration of prostaglandin I2 also led to a significant induction with the level similar to refeeding. The stimulatory effect of prostaglandin I2 was completely abolished by a specific and irreversible enzyme inhibitor, difluoromethylornithine. Prostaglandin E2 had a similar but lesser effect than prostaglandin I2 on the induction of the enzyme activity. Pretreatment with indomethacin, a cyclooxygenase inhibitor had no effect on feeding-associated enzyme induction. These results indicate that although exogenous prostaglandin I2 appears to be a potent stimulant for ornithine decarboxylase activity in rat small intestine, endogenous prostaglandins seem to play little or no role in feeding-associated induction of ornithine decarboxylase.