Morphine enhances gastric mucus synthesis in rats

The opioid peptide DAMME modulates histamine's content in gastric mucosa of the rat

The effects of a synthetic Met-enkephalin analogue D-Ala2, MePhe4Met(O)5-ol]enkephalin (DAMME) (1 mg/kg. IP) on gastric damage produced by necrotizing agents (0.6 N HCl, ethanol 1 ml/rat, PO) were evaluated, and the correlation between histamine and opioids in stomach was investigated, Rats pretreated with DAMME bad significantly less severe lesions and lower histamine content in gastric tissue. The histamine level, expressed in mg/g of gastric tissue, changed from 0.41 +/- 0.10 of control animals to 1.33 +/- 0.12 for HCl and 1.51 +/- 0.20 for ethanol treatment, whereas in animals pretreated with DAMME the values were significantly reduced to 0.55 +/- 0.13 and 0.65 +/- 0.15. These results confirm a link between the gastroprotection produced by opioids and the modulation of histaminergic activity in the rat stomach.

Antisecretory and anti-ulcer effects of morphine in rats after gastric mucosal aggression

The effects of morphine on gastric secretion, barrier mucus and mucosal lesions were studied in pylorus-ligated rats treated with the ulcerogenic agents, indomethacin, aspirin or taurocholic acid. All three ulcerogenic agents induced significant mucosal lesions. Morphine decreased gastric acid secretion and suppressed the aspirin- and taurocholic acid-induced, but not the indomethacin-induced mucosal lesions. These results suggest that the ulcerogenic mechanisms of indomethacin and the other agents are not identical. Moreover the antiulcer effect of morphine appears to be mediated by an increased barrier mucus level: the amount of Alcian blue bound to the mucosa, an indirect estimate of the adherent mucus layer, was increased by morphine and correlated with its protective effect. All morphine effects were reversed by naloxone.

Effects of morphine, hypoxaemia and hypercapnia on the rat stomach

The effects of morphine, hypoxaemia or hypercapnia on gastric acid secretion, gastric mucus synthesis and the gastric mucosa were studied in conscious rats with pyloric occlusion. Hypoxaemia and hypercapnia were induced by morphine 32 mg/kg given i.p., or each condition was produced separately by adjusting the composition of respired air in the chamber where the animals were kept during the experimental period. Hypoxia significantly enhanced gastric mucus synthesis whereas hypercapnia significantly reduced gastric acid secretion. These effects were significantly alleviated by atropine pretreatment. Morphine-treated rats exhibited decreased gastric acid secretion, increased gastric mucus synthesis and a higher mean ulcer index but only the reduced gastric acid output was significantly prevented by atropine. It is suggested that the effect of morphine on gastric acid secretion may result from its respiratory depressant action and consequent acute stress production. However, the mechanisms by which morphine can increase mucus synthesis and produce ulceration remain obscure.