PERMISSIVE ROLE OF ANGIOTENSIN II IN MANTENANCE OF ENDOTHELIUM-DEPENDENT VASODILATION IN CEREBRAL MICROCIRCULATION

Abstract

Objective: A number of data suggest, rather controversial, permissive role of angiotensin II (ANGII) in maintaining vasodilator responses in microcirculation, via its interaction with AT1 receptors (AT1R). This study aimed to determine the role of ANGII and AT1R in the mechanisms of flow-induced dilation (FID) in middle cerebral arteries (MCA) and incidence of oxidative stress at the functional, cellular and molecular level in the cerebral vasculature and in the serum of Sprague-Dawley (SD) rats fed high salt diet (HS). Design and method: Eleven-week old, male SD rats were randomly assigned to control group (CTRL, 0.4% NaCl in rat chow); Losartan group (rats on a standard diet given the AT1R blocker losartan (1 mg/mL) in drinking water); HS group (7 days 4% NaCl in rat chow) or HS+ANGII group (7 days HS with 3 days ANGII administration via osmotic minipumps (100 ng/kg/min on days 4–7)). FID of MCA was determined in absence/presence of the NOS inhibitor L-NAME, the non-selective cyclooxygenases inhibitor indomethacin, and the superoxide dismutase mimetic TEMPOL. Gene and protein expression of antioxidative enzymes and enzymes involved in FID mechanisms were determined by RT-qPCR and western blot. Vascular NO and superoxide/ROS levels were assessed by direct fluorescence. Serum systemic oxidative stress parameters was measured by spectrophotometry. All experimental procedures conformed to the EU Directive 2010/63/EU. Results: HS or AT1R blockade impaired FID and increased oxidative stress. Supplementation of ANGII restored the mechanisms of FID in MCA of rats fed HS diet to the ones present in CTRL rats without affecting arterial blood pressure by decreasing systemic oxidative stress and decreasing superoxide/ROS levels and increased NO bioavailability in the vascular wall of HS treated rats. The AT1R blockade resulted in significantly attenuated endothelium-dependent dilation, changed mechanisms of FID, increased vascular and systemic oxidative stress and decreased expression/ activity of antioxidative enzymes. Conclusions: ANGII is crucial in the preservation of vascular oxidative stress-antioxidant system balance and via AT1R, in maintenance of physiological vasodilation mechanisms of MCA. Suppression of ANGII is a key link between HS intake and development of endothelial dysfunction, and impaired regulation of cerebral blood flow.