Haemodynamic effects of the flavonoid quercetin in rats revisited.

The flavonoid quercetin increased the in vitro potency of the alpha-blocker tamsulosin to antagonize phenylephrine-dependent arterial contractions 10-fold. To examine if this supplement-drug interaction luxates hypotensive and orthostatic events in vivo, several sets of studies were conducted in hypertensive (SHR) and normotensive (WKY) rats.First, in rats pretreated with quercetin or its vehicle, (de)pressor responses to phenylephrine and tamsulosin were examined. Secondly, tamsulosin-induced changes in renal, mesenteric, hindquarter, and carotid conductance were compared in quercetin and vehicle treated rats instrumented with Doppler flow probes. Animals were also placed on a tilt table to record regional haemodynamic changes to orthostatic challenges. Thirdly, adult SHR were instrumented with telemeters to measure 24h patterns of blood pressure. Recordings were made before and during a 5 weeks oral treatment of quercetin. Finally, prehypertensive SHR were treated with quercetin from 4-8 weeks of age and arterial pressure was measured at 8 and 12 weeks.Pretreatment with quercetin did not influence (de)pressor responses to phenylephrine and tamsulosin, neither in WKY or SHR. While tamsulosin treatment and tilting lowered blood pressure and increased conductances in all vascular beds, effect size was not influenced by pretreatment with quercetin. Prolonged treatment with quercetin, either in prehypertensive SHR or adult SHR with established hypertension did not lower blood pressure.Cumulatively, these data demonstrate that quercetin does not amplify haemodynamic effects of tamsulosin or tilting in vivo in rats, and has no effect on blood pressure development in SHR.