PURPOSE: Palmatine is an isoquinoline alkaloid, with multiple pharmacological actions, including anti-inflammatory activity. The aim of this study was to examine the effect of palmatine on the prostatic urethral pressure in anesthetized rabbit. MATERIALS AND METHODS: 10-week-old male New Zealand White rabbits (3.0-3.5kg) were used in the experiment. After anesthetized with urethane (800mg/kg i.v.), a midline incision was made, and the urinary bladder completely drained. To prevent filling of the bladder, polyethylene tubes were inserted into the bilateral ureters. Using a 3-F MIKRO-TIP catheter transducer positioned in the prostatic urethra, urethral pressure was recorded continuously. To record the blood pressure, the left femoral artery was cannulated with an angiocatheter. After a stabilizing period, phenylephrine (1mug/kg) was intravenously administered two or three times. When the increase in the urethral pressure became stable, palmatine was administered intravenously (0.5-3.0mg/kg), followed by phenylephrine, with no time interval. RESULTS: In the anesthetized rabbits, an intravenous bolus injection of palmatine (0.5-3.0mg/kg) caused no significant change in the resting prostatic urethral pressure (p>0.05), but decreased the blood pressure (p<0.05). After administration of phenylephrine, the urethral pressure increased from 7.5 0.8 mmHg to 26.5 2.6 mmHg, with the difference in the pressure (19.0 3.1 mmHg) being statistically significant (p<0.01). The intravenously administered palmatine (0.5-3.0mg/kg) dose-dependently inhibited the phenylephrine-induced increases in the prostatic urethral pressure and mean blood pressure. The maximal inhibition was obtained when a palmatine dose of 3.0mg/kg was administered, at which point, the decrease in the urethral pressure was 73.1% (p<0.01). CONCLUSIONS: These results indicate that palmatine inhibits the phenylephrine-induced increases in the prostatic urethral pressure and blood pressure in the anesthetized rabbits.