Effects of mu- and kappa-opioid receptor agonists on urinary output in mice.

The effects of ethylketazocine, morphine, bremazocine and naloxone were determined on urinary output and weight loss in Cox mice. Morphine and fentanyl were also studied in Harlan mice. Bremazocine, ethylketazocine and morphine markedly increased urinary output and weight loss within 5 hr after injection. Naloxone antagonized the diuretic actions of morphine (5 mg/kg) and bremazocine (0.06 mg/kg) over a similar dose range (0.3--10 mg/kg). By comparison with the other agonists, fentanyl had little effect on urinary output or weight loss. These results suggest that kappa agonist activity increases urinary output in mice just as reported for rats. The data also suggest that in mice morphine has some kappa agonist activity, whereas fentanyl does not.