Abstract Body: Angiotensin II type 1 receptor (AT₁R) is a member of the seven-transmembrane G-protein-coupled receptor (GPCR) superfamily, which is the largest class of drug targets. AT₁R adopts different conformations that can either bias G-protein coupling (particularly Gaq) or b-arrestin signaling. Evidence suggests that Angiotensin II (ANG) AT₁R-induced β-arrestin signaling is cardioprotective, whereas prolonged Gaq-dependent signaling is detrimental. We hypothesize that prolonged activation of the AT₁R/Gaq pathway in vascular smooth muscle (SMC) leads to elevated blood pressure and vascular dysfunction. We generated an AT₁R mutant (AT₁R^TSTS-AAAA) that prevents phosphorylation of several C-terminal residues by GPCR kinases leading to impaired b-arrestin recruitment and prolonged Gaq-biased signaling. Transgenic mice were generated with a construct that induces both AT₁R^TSTS-AAAA and tdTomato expression in response to CRE-recombinase. Mice carrying AT₁R^TSTS-AAAA were bred with tamoxifen-inducible SMC-specific CRE (SMC^CRE, S-TSTS) mice. Tamoxifen successfully activated the transgene as evidenced by expression of the embedded tdTomato reporter. One week after tamoxifen, S-TSTS mice exhibited an increased in systolic blood pressure (SBP, 147.8±13.2 vs. 108.9±4.6 mmHg). Once hypertension (HT) was established, candesartan (10 mg/kg/day in drinking water) was administered. HT was effectively reversed in the S-TSTS mice 1-week post-candesartan. SBP became elevated in S-TSTS mice (142.0± 7.7 vs. 90.4±1.1 mmHg, p<0.05) two weeks after ending candesartan. Mesenteric arteries from S-TSTS mice exhibited a decrease in vasodilation to acetylcholine (ACh, p<0.05), that was reversed after preincubation with Tempol and ROCK inhibitor (p<0.05). Pretreatment with the NOS inhibitor L-NAME completely inhibited ACh-induced relaxation in both groups, suggesting that restoration of vasodilation in S-TSTS mice was due to a restoration of the NO-dependent pathway (p<0.05). In addition, S-TSTS mice exhibited enhanced ANG-induced vasoconstriction (p<0.05), which was inhibited by preincubation with losartan (p<0.05), indicating an AT₁R-dependent mechanism. Our findings suggest that hyperactive AT₁R-mediated G-protein and/or a deficiency of β-arrestin signaling in SMC results in HT and vascular dysfunction through oxidative stress and ROCK signaling pathway.