The effect of phenylpropanolamine on the urethral pressure and heart rate is retained after repeated short-term administration in the unanaesthetized, conscious dog.

The present study was performed to test whether high dose agonist (phenylpropanolamine) administration twice a day causes desensitization of urethral alpha-adrenoceptors in vivo. Urethral pressure was measured on five consecutive days of phenylpropanolamine treatment of the unanaesthetized, conscious dog, and the method is described in detail. Phenylpropanolamine hydrochloride proper (75 mg, 5.1-6.1 mg kg-1), and a sustained-release formulation, both significantly increased urethral pressure and decreased heart rate. Interruption of administration for two to three days did not alter the effect. The present results suggest that the effect of phenylpropanolamine was retained, and that the alpha-adrenoceptors of dog urethra did not desensitize after repeated administration of the alpha-adrenoceptor agonist phenylpropanolamine twice a day.