Angiotensin-(1-7)–Stimulated Nitric Oxide and Superoxide Release From Endothelial Cells

-The stimulation of endothelium-dependent NO release by angiotensin-(1-7) Ang-(1-7) has been indirectly shown in terms of vasodilation, which was diminished by NO synthase inhibition or removal of the endothelium. However, direct measurement of endothelium-derived NO has not been analyzed. With a selective porphyrinic microsensor, NO release was directly assessed from single primary cultured bovine aortic endothelial cells. Ang-(1-7) caused a concentration-dependent release of NO of 1 to 10 µmol/L, which was attenuated by NO synthase inhibition. D-Ala(7)Ang-(1-7) (5 µmol/L), described as a selective antagonist of Ang-(1-7) receptors, inhibited Ang-(1-7)-induced NO release only by approximately 50%, whereas preincubation of bovine aortic endothelial cells with the angiotensin II subtype 1 and 2 receptor antagonists EXP 3174 and PD 123,177 (both at 0.1 µmol/L) led to an inhibition of 60% and 90%, respectively. A complete blockade of the Ang-(1-7)-induced NO release was observed on preincubation of the cells with 1 µmol/L concentration of the bradykinin subtype 2 receptor antagonist icatibant (HOE 140), suggesting an important role of local kinins in the action of Ang-(1-7). Simultaneous direct measurement of superoxide (O(2)(-)) detected by an O(2)(-)-sensitive microsensor revealed that the moderately Ang-(1-7)-stimulated NO release was accompanied by a very slow concomitant O(2)(-) production with a relative low peak concentration in comparison to the O(2)(-) production of the strong NO releasers bradykinin and, especially, calcium ionophore. Thus, Ang-(1-7) might preserve the vascular system, among others, due to its low formation of cytotoxic peroxynitrite by the reaction between NO and O(2)(-).