The Action of Intrathecal Morphine and Methadone on the Lower Urinary Tract in the Dog

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Abstract
The effects of intrathecally administered morphine and methadone on lower urinary tract dynamics were investigated by cystometrograms and urethral pressure profiles in 16 anesthetized dogs. The examinations were performed before and 30, 60 and 90 minutes following intrathecal injection of 0.03 mg/kg morphine or methadone. Intrathecal normal saline was used for control studies. Significant relaxation of the detrusor was noted after intrathecal morphine as expressed by a decrease in mean intravesical pressure (p < 0.05) and by a rise in the calculated detrusor compliance. These effects were reversed by intravenously injected naloxone. As opposed to morphine, methadone caused an increase in detrusor tone. No appreciable effects were observed on the urethra after intrathecal morphine or methadone. Neither intravenous injection of the opiates nor intrathecal administration of saline caused alterations in bladder tone. The result may imply a spinal, albeit opposing, effect of the two opiates on bladder dynamics.