Dopaminergic mechanisms controlling urethral function in rats

Aims: To investigate the role of dopamine receptor subtypes in the control of urethral activity. Methods: Simultaneous recordings of intravesical and urethral perfusion pressure (UPP) were performed in rats under urethane anesthesia. Changes in coordinated activity of the bladder and urethral sphincter were examined following intravenous (i.v.), intrathecal (i.t.), or intracerebroventricular (i.c.v.) administration of dopamine D1- and D2-like receptor agonists (SKF38393 and quinpirole, respectively) and antagonists (SCH23390 and remoxipride, respectively). Results: Quinpirole (0.03, 0.1, and 0.3 mg/kg i.v.) dose-dependently decreased baseline urethral pressure to 45.33 +/- 5.8, 33.7 +/- 3.3 (P < 0.05, n = 6), and 27.7 +/- 3.3 cm H2O (P < 0.05, n = 5) from the control value (46.0 +/- 4.0 cm H2O), respectively. i.c.v. injection of quinpirole (1 mu g) decreased baseline urethral pressure to 33.6 +/- 5.0 cm H2O (P < 0.05, n = 4) from the control value (51.4 +/- 4.9 cm H2O) in contrast to the insignificant effects of i.t. administration of the drug (3 mu g). The decrement of baseline pressure induced by quinpirole (0.1 mg/kg i.v.) was suppressed by a-bungarotoxin (BGT), a neuromuscular blocking agent. SCH23390 (1 and 3 mg/kg, i.v.) dose-dependently decreased the frequency of high frequency oscillation (HFO) of the urethral sphincter. SKF38393 or remoxipride did not have significant effects on any parameters of bladder and urethral activity. Conclusions: These results indicate that activation of D2-like dopamine receptors at a supraspinal site can suppress activity of the striated muscle urethral sphincter. Thus, decreased urethral resistance induced by D2 dopamine receptor activation might aggravate urge incontinence symptoms often seen in patients with Parkinson's disease (PD).