Naloxone is protective against indomethacin-induced intestinal ulceration in the rat.

Naloxone, an opiate antagonist, was reported to protect against stress ulcers in dogs and rats. We studied its possible protective effect against indomethacin-induced intestinal ulceration in the rat. Naloxone was indeed found to possess a marked protective effect on the intestinal mucosa (ulcer index 73.3 +/- 13.6 vs. 273.8 +/- 21.8, p less than 0.001). Naloxone was found to elevate basal intestinal mucosal prostaglandin E2 (p less than 0.001) and cyclic adenosine monophosphate levels (p less than 0.005) but was unable to overcome the inhibition of prostaglandin E2 caused by indomethacin. An increase of cyclic adenosine monophosphate levels was seen, however, even in the presence of indomethacin, suggesting that cyclic adenosine monophosphate, but not prostaglandins, may play a role in the protective effect of naloxone.