Effect of quercetin on tachykinin-induced plasma extravasation in rat urinary bladder

The effect of quercetin on substance P-induced plasma extravasation in rat urinary bladder and its modulation by endogenous peptidases in conscious rats was studied. Plasma protein extravasation (PE) was assayed by measurement of extravasated Evans blue dye (microg/g dry tissue). Intravenous injection of substance P (SP, 10 nmol/kg) significantly increased PE in the urinary bladder. PE evoked by SP was increased significantly by quercetin (20 mg/kg, p.o.) pretreatment in the urinary bladder (73.5 +/- 4.9 to 152.2 +/- 9.9). Pretreatment with captopril, an angiotensin-converting enzyme (ACE) inhibitor (10 nmol/kg, i.v.), or with phosphoramidon, a neutral endopeptidase (NEP) inhibitor (2.5 micromol/kg, i.v.) also potentiated the SP-induced PE in urinary bladder, 286.2 +/- 20.4 and 323.3 +/- 34.0, respectively. Quercetin did not show any effect on neurokinin-A (NKA, 10 nmol/kg, i.v.) -induced plasma extravasation. The present study demonstrates that quercetin potentiates the PE induced by substance P in the urinary bladder. These effects suggest that this flavonoid might cause inhibition of NEP and/or ACE.