16,16-Dimethyl prostaglandin E2 suppresses the increases in the proliferative activity of rat colonic epithelium induced by indomethacin and aspirin

Abstract

Treatment of rats with indomethacin rapidly increased ornithine decarboxylase (4 h) of colonic mucosa and [3H]thymidine incorporation into coJonic mucosal deoxyribonucleic acid (DNA) (1 or 5 days) when this parameter was examined in vivo and ex vivo. The changes in colonic mucosal ornithine decarboxylase and DNA synthesis induced by indomethacin were correlated temporally with suppression of colonic prostaglandin synthesis, as assessed from ex vivo colonic production of prostaglandin E, the dominant prostaglandin product of colon. Autoradiographic studies indicated that the enhancement of proliferative activity of colonic epithelium after treatment with indomethacin for 1 day was confined to the lower third of the colonic crypt (normal proliferative zone). After 5 days of indomethacin treatment, however, there was an extension of the proliferative zone to the upper third of the colonic crypts. Concurrent treatment of rats with the stable prostaglandin E2 analogue, 16,16-dimethyl prostaglandin E2, suppressed indomethacin-induced increases in colonic mucosal ornithine decarboxylase and DNA synthesis. Concurrent administration of 16,16-dimethyl prostaglandin E2 also prevented the extension of the proliferative zone of colonic epithelium induced by 5 days of indomethacin administration. 16,16-Dimethyl prostaglandin E2 alone for 1–5 days had no detectable effects on colonic mucosal ornithine decarboxylase and DNA synthesis compared with corresponding control values. Increases in colonic mucosal DNA synthesis were also induced by treatment of rats for 5 days with aspirin (ASA). The stimulation of colonic mucosal DNA synthesis induced by ASA was significantly suppressed by concurrent administration of 16,16-dimethyl prostaglandin E2 and was also correlated with the inhibition of colonic prostaglandin synthesis by ASA. The colons of rats treated with indomethacin for 1 day or ASA for 5 days appeared normal by light microscopy. However, treatment of rats for 5 days with indomethacin resulted in mild to moderate inflammation of the lamina propria and some goblet cell depletion at the mucosal surface, but no loss of surface epithelium. The ultrastructure of the surface epithelium of the colons of rats treated with indomethacin or ASA was normal as assessed by electron microscopy. The results thus demonstrate that inhibition of local colonic prostaglandin synthesis is associated with increases in the proliferative activity of colonic epithelium, and that these increases are suppressed by administration of 16,16-dimethyl prostaglandin E2. Under some conditions, the increases in proliferative activity that were observed with indomethacin and ASA are dissociated from drug-induced inflammation and cell surface injury.