Insulin sensitivity is partly dependent on
insulin-mediated
nitric oxide (NO) release and
antioxidants may decrease
insulin resistance by amelioring NO bioavailability. The effects of chronic
therapy with the
antioxidant quercetin on blood pressure, vascular function and
glucose tolerance in male spontaneously hypertensive rats (SHR), a model of genetically
hypertension and
insulin resistance, were analyzed. Rats were divided into four groups, WKY vehicle, WKY
quercetin, SHR vehicle and SHR
quercetin. Animals were daily administered by gavage for four weeks: vehicle,
quercetin in vehicle (10mg/kg
body weight). Blood pressure was followed by tail-cuff plethysmography. Chronic
quercetin treatment reduced systolic blood pressure, and significantly reduced left ventricular (-10%) and renal (-6%)
hypertrophy. However, oral
glucose tolerance test, homeostatic model assessment of
insulin resistance, total
cholesterol and
triglycerides were unaffected by
quercetin in both strains of rats. It also improved the blunted aortic endothelium-dependent relaxation to
acetylcholine, without affecting both endothelium-dependent relaxation to
insulin and endothelium-independent relaxation to
sodium nitroprusside in SHR. In WKY rats,
quercetin in vitro and in vivo, impaired the relaxation to
insulin.
Quercetin reduced both plasma
malondialdehyde levels and aortic
superoxide production in SHR. Furthermore,
quercetin inhibited
insulin-stimulated
protein kinase B (Akt)- and endothelial
NO synthase (eNOS) phosphorylation. In conclusion,
quercetin reduced blood pressure, left ventricular and renal
hypertrophy and improved NO-dependent
acetylcholine relaxation. However, and despite its
antioxidant effects,
quercetin was unable to improve
insulin sensitivity possibly through its specific interference with the
insulin signalling pathway.