To clarify the role of dopamine D1 and D2 receptors in the volume-induced m
icturition reflex, conscious, female rats were investigated cystometrically
before and after intravenous administration of SKF 38393 (a selective D1 r
eceptor agonist), SCH 23390 (a selective D1 receptor antagonist), quinpirol
e (a selective D2 receptor agonist), and remoxipride (a selective D2 recept
or antagonist). The effect of quinpirole was also investigated in the prese
nce of remoxipride. Intravenous administration of SKF 38393 (0.01-3.0 mg/kg
) did not affect any cystometric parameters investigated. On the other hand
, SCH 23390 (0.1-1.0 mg/kg i.v.) reduced bladder capacity and micturition v
olumes and increased the micturition pressure in a dose-dependent manner. Q
uinpirole (0.01-0.1 mg/kg) given intravenously, dose-dependently decreased
bladder capacity and micturition volumes. Pre-treatment with remoxipride (1
.0 mg/kg i.v.) significantly attenuated the effect of quinpirole (0.1 mg/kg
i.v..). Remoxipride (0.1-1.0 mg i.v.) itself did not cause any significant
changes in the cystometric parameters. These results suggest that in consc
ious rats, DI receptors tonically inhibit the micturition reflex and that D
2 receptors are involved in facilitation of the micturition reflex. It may
be speculated that detrusor hyperreflexia associated with Parkinson's disea
se results fi om activation failure of D1 receptors and that administration
of D2 receptor agonists might worsen the condition. Neurourol. Urodynam. 2
0:105-113. 2001. (C) 2001 Wiley-Liss. Inc