Spinal opioid receptors and inhibition of urinary bladder motility in vivo

The effects of intrathecal injections of morphine and other opioid receptor selective drugs were tested on urinary bladder contractions in the anesthetized rat. Morphine produced dose-related inhibition of bladder motility which was abolished by naloxone. This action was also observed with mu- and delta-opioid receptor agonists but not with a kappa-opioid receptor agonist. These observations appear related to the urinary retention seen clinically with epidural administrations of morphine and support the hypothesis that urinary bladder activity is influenced by spinal opioid mechanisms involving mu- and delta-opioid receptors.