Aim: 

Angiotensin (Ang)-(1-7) is a heptapeptide with endothelium-dependent vasorelaxant properties, acting through the G protein-coupled receptor Mas. We investigated whether the inhibition of the Ang-(1-7)/Mas axis could be responsible for endothelial dysfunction.

Methods: 

Vascular reactivity was assessed in mesenteric arteries from C57B1/6 mice with a genetic Mas deletion and matched wild-type animals using a small-vessel myograph. In cultured human umbilical vein endothelial cells (HUVEC), NO release was measured by the Griess method, endothelial nitric oxide synthase (eNOS) levels were measured by western blot. The levels of L-arginine and its derivatives asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA), considered as eNOS inhibitors, were determined by HPLC.

Results: 

Ang-(1-7) (1 pM-1mM)-mediated relaxation was impaired in both arteries from Mas-deficient mice and wild-type arteries pre-treated with the Mas receptor antagonist D-Ala-Ang-(1-7) (A779, 1 mM). Interestingly, the responses to other endothelium-dependent vasodilators, like bradykinin (BK) and acetylcholine (both at 1 nM-30 mM), were also impaired, while endothelium-independent relaxant responses to sodium nitroprusside (1 nM -10 mM) were unaltered. In HUVEC, BK (1 mM)-mediated NO release was increased by pre-treatment with Ang-(1-7) (100 nM) for 72 h, while it was abolished by pre-treatment with A779 (1 mM). Indeed, A779 pre-treatment did not modify total eNOS, but it reduced phospho-Ser1177-NOS (active form) levels, while enhancing phospho-Thr495-eNOS (inactive form) levels. Additionally, the ADMA/L-Arg and SDMA/L-Arg ratios were increased.

Conclusions: 

These results suggest a pivotal role of Mas receptor in maintaining normal vascular tone and endothelial function.