Morphine inhibits the carrageenan-induced oedema and the chemoluminescence of leucocytes stimulated by zymosan.

Morphine inhibited the oedema formation induced by carrageenan. The anti-inflammatory activity developed 120 min after carrageenan injection, suggesting that inhibition of the kinin phase might be partly responsible. This assumption is supported by the findings that morphine inhibited bradykinin oedema but did not influence oedema formation induced by histamine, 5-HT or PGE2. The anti-inflammatory activity of morphine was partially inhibited by naloxone (0.5-1 mg kg-1) in the carrageenan oedema test. Zymosan-stimulated chemoluminescence of neutrophils of the rat was inhibited both by morphine (0.1-10 microM) and naloxone (1-100 microM). When morphine and naloxone were administered simultaneously (10 microM) their inhibitory effects were additive. Naloxone also failed to antagonize the inhibitory action of morphine in lower dose (0.1 microM). These results suggest that the effect of morphine in inflammation might be mediated either by one of the opiate receptor subtypes insensitive to naloxone or a non-opiate mechanism might be involved.