Urodynamic studies after intrathecal administration of baclofen and morphine in dogs.

The effects of intrathecally administered baclofen and morphine on the lower urinary tract dynamics of anesthetized dogs were investigated by means of cystometrogram and urethral pressure profile measurement. The experiments were performed prior to and 30, 60 and 90 minutes following intrathecal injection of either baclofen (0.03 mg./kg.), morphine (0.03 mg./kg.), or a mixture of the two (0.03 mg./kg. of each drug). Vesical pressure was significantly depressed after either baclofen (p less than 0.005) or morphine (p less than 0.005), while urethral pressure was decreased significantly only following baclofen (p less than 0.025). Administration of a baclofen/morphine admixture resulted in an additive reaction on the urethral pressure profile, compared with the changes brought about by each drug alone. Relaxation of the bladder and reduction in urethral resistance occurred 30 minutes post injection, increasing progressively after 60 and 90 minutes. The results demonstrated that baclofen, by its influence on cord neuron interaction, is capable of inhibiting the activity of the smooth muscle of the normal bladder and urethra, which in the case of the latter became more pronounced when both drugs were administered simultaneously by the intrathecal route.