S-NITROSOGLUTATHIONE INHIBITS CEREBROVASCULAR ANGIOTENSIN II DEPENDENT AND INDEPENDENT AT 1 RECEPTOR RESPONSES: A POSSIBLE ROLE OF S-NITROSATION.

BACKGROUND AND PURPOSE: Angiotensin II (AngII) and nitric oxide (NO) regulate cerebral circulation. AngII AT1 receptors exert ligand-dependent and -independent (myogenic tone, MT) vasoconstriction of cerebral vessels. NO induces post-translational modifications of proteins such as S-nitrosation (redox modification of cysteine residues). In cultured cells, S-nitrosation decreases AngII affinity for AT1 . The present work evaluated the functional consequences of S-nitrosation on both AngII-dependent and AngII-independent cerebrovascular responses.

EXPERIMENTAL APPROACH: S-nitrosation was induced in isolated rat middle cerebral arteries by pretreatment with the NO donors, S-nitrosoglutathione (GSNO) or sodium nitroprusside (SNP). Agonist-dependent activation of AT1 was evaluated by concentration response curves to AngII. Ligand-independent activation of AT1 was evaluated by calculating MT (active vs. passive diameter) at pressures ranging from 20 to 200 mmHg in the presence or not of a selective AT1 inverse agonist.

KEY RESULTS: GSNO or SNP completely abolished the AngII-dependent AT1 vasoconstriction of cerebral arteries. GSNO had no impact on other vasoconstrictors sharing (phenylephrine, U46619) or not (serotonin) the same signaling pathway. MT was reduced by GSNO and addition of losartan did not further decrease MT, suggesting that GSNO blocks AT1 -dependent MT. Ascorbate (which reduces S-nitrosated compounds) restored AngII-response, but not the sGC inhibitor ODQ, thus suggesting that these effects are mediated by S-nitrosation rather than by S-nitrosylation.

CONCLUSION: In rat middle cerebral arteries, GSNO pretreatment specifically affects the AT1 receptor and reduces both AngII-dependent and AngII-independent activations, most likely through AT1 S-nitrosation.