BACKGROUND: Morphine exerts immunomodulatory effects dependent on several factors including species and parameter examined. The aim of this study was to assess the influence of morphine on experimental peritonitis and leukocyte activity in young chickens of both sexes.
METHODS: Peritonitis was elicited by intraperitoneal injection of thioglycollate (TG) alone or supplemented with morphine; additional chicken groups were injected with morphine alone. Morphine-treated birds (with or without elicited peritonitis) were pretreated with naltrexone, an antagonist of opioid receptors. Control groups were intact or PBS-injected. At specific postinjection intervals peritoneal leukocytes (PTL) were obtained by flushing the peritoneal cavity, counted and used for in vitro assays of activity (respiratory burst). Vascular permeability was measured using Evans blue solution.
RESULTS: Inflammatory reaction and morphine influence were gender-dependent: the extent of TG-induced peritonitis was higher in males and it was additionally stimulated by morphine. This pro-inflammatory effect of morphine was not seen in females. PTL collected from morphine-treated chickens of both sexes exhibited a stronger nitroblue tetrazolium reduction than in non-treated birds and this effect was antagonized by naltrexone.
CONCLUSIONS: The effect of morphine on peritonitis in chickens appears different to that in other vertebrate species, although the mechanism(s) of its influence on leukocyte activity are similar.