Protection by opioids against gastric lesions caused by necrotizing agents.

The synthetic opioid met-enkephalin analog [D-Ala2, MePhe4, Met(0)5ol] enkephalin (DAMME) and the opiate morphine injected intraperitoneally to rats at doses of 0.5-2 and 5-20 mg/kg, respectively, showed a protective effect on gastric damage induced by oral administration of necrotizing agents (0.6 N HCl or 0.2 N NaOH solutions, 1 ml/rat). The protection was prevented by naltrexone (10 mg/kg s.c.), an opioid antagonist with long-lasting activity. Histological sections of mucosal samples from animals pretreated with morphine (10 mg/kg i.p.) and DAMME (1 mg/kg i.p.) showed less alteration of the columnar epithelium, with a normal glandular structure, than untreated rats. A mediation of prostaglandins is suggested, since indomethacin (10 mg/kg s.c.) significantly reduced the protective effects of opioids.