Morphine modulation of peritoneal inflammation in Atlantic salmon and CB6 mice

Peritoneal inflammation is a convenient model for comparisons of modulatory effects of morphine in phylogenetically distant vertebrates. Both in salmo n and mice morphine injected intraperitoneally together with an irritant (t hioglycolate) significantly inhibits inflammation as estimated Ly the numbe r of peritoneal leukocytes, The low number of exudate cells in morphine-tre ated animals seems to be compensated Ly their high activity, as evidenced L y the enhanced phorbol myristate acetate-induced respiratory burst. The mor phine-inhibited influx of leukocytes into the irritated peritoneal cavity c orrelates with the morphine-lowered level of plasma chemotactic factors bot h ill fish and mice, It implies that morphine impairs the level of plasma c hemotactic factor either directly (affecting their release from the residen t peritoneal cells) or indirectly (decreasing the number of inflammatory le ukocytes by inhibition of their migration from hemopoietic sites). The inhi bitory effects of morphine on both the cell number and chemoattractant leve l are completely reversed Ly the naltrexone pretreatment,,which implicates the involvement of opioid receptors.