Objective: The angiotensin II (AngII)-infused apolipoprotein E-deficient (ApoE(-/-)) mouse model is widely used to study atherosclerosis and abdominal aortic aneurysm. An increase in blood pressure has been reported in this model however the underlying mechanism has not been fully explored. In this study, we investigated whether vasomotor dysfunction develops in AngII-infused ApoE(-/-) mice and the underlying mechanism involved.
Methods: ApoE(-/-) mice were infused with vehicle (distilled water) or AngII subcutaneously for 14 days. Blood pressure and heart rate were measured using the non-invasive tail cuff method. Aortic vascular reactivity and expression of key proteins (endothelial nitric oxide synthase (eNOS), phospho-eNOS and caveolin-1) were assessed using tension myography and Western blotting respectively. Plasma nitric oxide (NO) level was estimated using a colorimetric assay.
Results: AngII infusion caused a time-dependent increase in blood pressure (P<0.001). Aortas from AngII-infused mice were significantly less responsive to acetylcholine-induced endothelium-dependent relaxation when compared to aortas from mice infused with vehicle control (P<0.05). Contractile responses to phenylephrine (P<0.01) and potassium chloride (P<0.001) were significantly enhanced in aortas from AngII-infused mice. eNOS phosphorylation was significantly decreased in the aorta of AngII-infused mice (P<0.05). Aortic caveolin-1 protein expression was significantly increased in AngII-infused mice (P<0.05). Plasma nitrate/nitrite level was significantly reduced in AngII-infused mice (P<0.05). Pharmacological disruption of caveolae using methyl-β-cyclodextrin (MβCD) in isolated aortas from AngII-infused mice caused a significant leftward shift of the acetylcholine-induced relaxation concentration-response curve when compared to vehicle control (P<0.05).
Conclusion: Upregulation of caveolin-1 protein expression and reduced NO bioavailability contributes to aortic endothelial dysfunction in AngII-infused ApoE(-/-) mice.