Effects of kappa-opioid receptor agonists and morphine on food intake and urinary output in food-deprived and nondeprived rats

The effects of kappa-opioid receptor agonists, bremazocine, U-50, 488H and tifluadom and of a mu-opioid receptor agonist, morphine, on food intake and urinary output in food-deprived and nondeprived Sprague-Dawley rats was determined. In food-deprived animals, intraperitoneal administration of bremazocine at 0.1 mg/kg increased food intake but at 1.0 and 10.0 mg/kg doses decreased it. Tifluadom (0.1-10.0 mg/kg) had no effect on food intake. U-50,488H at 1.0 mg/kg increased food intake, whereas 10.0 mg/kg dose decreased the food consumption. In nondeprived rats, the kappa-opioid receptor agonists failed to produce any effect on food consumption. In food-deprived rats, all the three kappa-opioid receptor agonists increased the urinary output at the highest dose (10 mg/kg). In nondeprived rats similar effects as in food-deprived rats were observed except bremazocine increased urinary output at all the doses used. These results with kappa-opioid agonists may be related to either the existence of more than one population of kappa-opioid receptors or their differential actions at the opioid receptor types.