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 ra ts was studied. Plasma protein extravasation (PE) was assayed by measuremen t of extravasated Evans blue dye (mug/g dry tissue). Intravenous injection of substance P (SP, 10 nmol/kg) significantly increased PE in the urinary b ladder. 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) inhibi tor (10 nmol/kg, i.v.), or with phosphoramidon, a neutral endopeptidase (NE P) inhibitor (2.5 mu mol/kg, i.v.) also potentiated the SP-induced PE in ur inary bladder, 286.2 +/- 20.4 and 323.3 +/- 34.0, respectively. Quercetin d id not show any effect on neurokinin-A (NKA, 10 nmol/kg, i.v.) -induced pla sma extravasation. The present study demonstrates that quercetin potentiate s the PE induced by substance P in the urinary bladder. These effects sugge st that this flavonoid might cause inhibition of NEP and/or ACE. Copyright (C) 2001 John Wiley & Sons, Ltd.