EFFECTS OF MORPHINE AND LIPOSOMAL MORPHINE IN A MODEL OF INTESTINAL INFLAMMATION IN MICE

We have investigated the antitransit effects of free and liposomal mor phine in a model of intestinal inflammation, Mice received saline or c roton oil orally, 3 h prior to evaluation, and gastrointestinal transi t was measured 20 min afterwards. Peak/duration of effects, potency (E D(50)) and antagonism by naloxone and naloxone methiodide were evaluat ed. Peak effects occurred 30 and 40 min after administration of morphi ne and liposomal morphine, respectively, Encapsulated morphine had a m ore pronounced and prolonged effect than morphine, Comparison of the E D(50)s demonstrated that the potency of liposomal morphine was 3.5 tim es higher than that of morphine during inflammation; in addition, infl ammation increased the potency of morphine and liposomal morphine, 3 a nd 9.2 times, respectively, The effects of morphine and liposomal morp hine in croton oil-treated mice were reversed by naloxone and naloxone methiodide. The results show that during inflammation, the potency an d duration of the antitransit effects of morphine are significantly en hanced by encapsulation.