Physostigmine and naloxone reverse the effect of intrathecal morphine on the canine urinary bladder

Cystometrograms and urethral pressure profiles were used in 11 anaesthetized dogs to study the urodynamic effects of intravenously administered physostigmine (Group I--seven dogs) and intravenously administered naloxone (Group II--four dogs) following intrathecal morphine. In four of these dogs (Group III) intravenous physostigmine preceded the intrathecal morphine injection. In Groups I and II, intrathecal morphine 0.03 mg kg-1 caused a significant relaxation of the detrusor P less than 0.05), as expressed by a fall of 34.2 +/- 4.4% (SE) in mean intravesical pressure and a rise of 57 +/- 12.7% (SE) in calculated detrusor compliance at 90 min. Both physostigmine, 0.1 mg kg,-1 and naloxone, 0.025 mg kg,-1 given at this time completely abolished the influence of the narcotic on the bladder without changing urethral pressures. In Group III, physostigmine produced a marked rise in intravesical pressure (P less than 0.01) that was reversed by subsequent morphine. It is of interest that physostigmine, a potent cholinergic agent, and naloxone, a pure opiate antagonist, exert a similar action on bladder function.