Abstract-Mas codes for a G protein-coupled receptor that is implicated in angiotensin-(1-7) signaling. We studied the cardiovascular phenotype of Mas-deficient mice backcrossed onto the FVB/N genetic background using telemetry and found that they exhibit higher blood pressures compared with controls. These Mas Ϫ/Ϫ mice also had impaired endothelial function, decreased NO production, and lower endothelial NO synthase expression. Reduced nicotinamide-adenine dinucleotide phosphate oxidase catalytic subunit gp91 phox protein content determined by Western blotting was higher in Mas Ϫ/Ϫ mice than in controls, whereas superoxide dismutase and catalase activities were reduced. The superoxide dismutase mimetic, Tempol, decreased blood pressure in Mas Ϫ/Ϫ mice but had a minimal effect in control mice. Our results show a major cardiovascular phenotype in Mas Ϫ/Ϫ mice. Mas-deletion results in increased blood pressure, endothelial dysfunction, and an imbalance between NO and reactive oxygen species. Our animals represent a promising model to study angiotensin-(1-7)-mediated cardiovascular effects and to evaluate Mas agonistic compounds as novel cardioprotective and antihypertensive agents based on their beneficial effects on endothelial function. Key Words: Mas-deficient mice Ⅲ endothelial function Ⅲ Ang-(1-7) Ⅲ reactive oxygen species Ⅲ NO T he Mas protooncogene codes for a peptide receptor that transduces extracellular signals to G proteins. Although Mas was once thought to be an angiotensin (Ang) II receptor, recent studies have shown that it binds to the heptapeptide Ang-(1-7). 1,2 Indeed, most of the Mas-mediated effects counteract those described for Ang II. Recently, Mas has been characterized as a physiological antagonist of the Ang II receptor Ang II type 1 (AT 1 ) by forming hetero-oligomers. 3 Moreover, acting through Mas, Ang-(1-7) has been shown to reduce blood pressure, to inhibit cell growth and proliferation, and to produce cardioprotective effects. 4 -8 Mas is expressed in vascular endothelium, 9 which, at the same time, is an important site for Ang-(1-7) generation. 10 Ang-(1-7)-induced vasodilation is endothelium dependent and occurs through NO or prostaglandin production. 9 -11 Moreover, in rats, short-term Ang-(1-7) infusion improves in vivo endothelial function primarily via NO release. 12 Along with these findings, we have shown recently that, in Mastransfected Chinese hamster ovary and human aortic endothelial cells, Ang-(1-7) induces Mas-mediated release of NO through site-specific phosphorylation/dephosphorylation of endothelial NO synthase (eNOS). 13 Reactive oxygen species (ROS) function as intracellular and intercellular second messengers and modulate endothelial function. The balance between ROS and NO seems to be an important modulator for cardiovascular functions and thereby profoundly influences blood pressure regulation. Under pathological conditions, reduction of NO bioavailability, together with elevation of ROS content (oxidative stress), results in vascular dysfunction. 14 In fact, ...

1 Studies have shown that the angiotensin II (Ang II) AT 1 receptor antagonist, losartan, accentuates the orthostatic hypotensive response in anesthetized rats, and there is evidence indicating that this effect is not exclusively mediated by AT 1 receptors. 2 We investigated whether the pronounced orthostatic cardiovascular response observed in losartantreated rats involves an interference with angiotensin-(1-7) (Ang-(1-7)) receptors. 3 Urethane-anesthetized rats were submitted to orthostatic stress (901 head-up tilt for 2 min). Intravenous injection of losartan (1 mg kg À1 , n ¼ 9) significantly accentuated the decrease in mean arterial pressure (MAP) induced by head-up tilt (À3376% after losartan vs À1578% control tilt). This effect was accompanied by a significant bradycardia (À873% after losartan vs À373% control tilt). Another AT 1 antagonist, candesartan, did not potentiate the decrease of MAP and did not change the cardiac response induced by head-up tilt. Strikingly, administration of the Ang-(1-7) antagonist, A-779 (10 nmol kg À1 , n ¼ 5), totally reversed the bradicardiac effect caused by losartan and this effect was accompanied by a tendency towards attenuation of the hypotensive response caused by losartan. 4 These findings indicate that the marked orthostatic cardiovascular response is specific for losartan, and that it may be due, in part, to an interaction of this antagonist with Ang-(1-7) receptors, probably at the cardiac level.

This study evaluated the physiological importance of Angiotensin-(1-7) receptor Mas on reflex control of circulation. Experiments were performed in male Mas-knockout (Mas-KO) and Wild Type (WT) conscious mice (12-20 wk of age). Baroreceptor reflex was evaluated by the bradycardic response induced by phenylephrine (0.25 μg/5 μl, i.v.). Bezold-Jarisch reflex was evaluated by phenylbiguanide (0.5 μg/5 μl, i.v.) and chemoreflex by potassium cyanide (2.5 μg/5 μl, i.v.). Baseline mean arterial pressure was higher in Mas-KO (n=14) as compared with WT mice (n=18) (118±1 mmHg vs. 109±2 mmHg); however, heart rate was similar in both strains (615±30 bpm vs. 648±13 bpm). Baroreflex bradycardia was lower (0.78±0.44 ms/mmHg vs. 1.30±0.14 ms/mmHg) in Mas-KO compared with WT mice. The depressor (-17±5 mmHg vs. -45±6 mmHg) and bradycardic (-212±36 bpm vs. -391±29 bpm) components of the Bezold-Jarisch reflex were also lower in Mas-KO mice. In addition, chemoreflex pressor response (+20±3 mmHg vs. +12±0.8 mmHg) and bradycardic response (-250±74 bpm vs. -52±26 bpm) were significantly higher in Mas-KO. These results further advances previous studies by showing that the lack of Mas receptor induced important imbalance in the neural control of blood pressure, altering not only the baroreflex but also the chemo- and Bezold-Jarisch reflexes.