Naloxone Induced Micturition in Unanesthetized Paraplegic Cats

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Abstract
In chronic spinal cats 2-10 wk after transection of the spinal cord at the lower thoracic level (T12-T13), the administration of naloxone, an opiate antagonist, (32-500 .mu.g/kg i.p.), stimulated micturition. The total quantity of urine released after administration of naloxone ranged from 10-70% (mean 39%) of the initial bladder volume. The response to the drug occurred 5-10 min after injection and was characterized by repeated periodic expulsion of small quantities or urine (5-10 ml) which coincided with a pattern of hind-limb movement which resembled walking behavior. The effects of naloxone persisted for about 1 h. The motor activity following administration of naloxone was dependent on activation of bladder afferents since it did not occur when the bladder was empty. Naloxone also facilitated the release of urine induced by stimulation of somatic afferents. With repeated administration of naloxone, tolerance developed which was evident for several days. An endogenous opiate may have a tonic inhibitory role in regulation of micturition. Pharmacologic manipulation of this putative inhibitory mechanism may facilitate management of neurogenic bladder dysfunction [in humans].