Abstract Body: Premenopausal women benefit from estrogen's protective effects, including lower arterial stiffness than men of the same age. Despite estrogen's protective role, menopausal hormone therapy showed no cardiovascular benefits in the Women's Health Initiative. One theory is that the response to menopausal hormone therapy is modulated by the presence of pre-existing cardiovascular disease. Estrogen signals through nuclear estrogen receptors ERα and ERβ, and the membrane-bound G protein-coupled estrogen receptor (GPER). Our lab has shown that GPER induces protective cardiovascular effects including decreased blood pressure, protection from renal damage, and attenuation of arterial remodeling. In this study, we hypothesized that GPER deletion would attenuate the protective vascular effects of estrogen after menopause. Female C57Bl/6J wildtype (wt) and global GPER knockout (ko) mice underwent ovariectomy (OVX) at 46 weeks of age and concurrently administered estrogen (E) or vehicle (Veh). Angiotensin II (Ang II; 700 ng/kg/day) infusion was used to induce hypertension either four weeks prior (Ang-E) or at the time of OVX (E-Ang) to evaluate the impact of cardiovascular diseases preceding or coinciding with menopause. Blood pressure was measured by tail-cuff plethysmography and arterial stiffness was assessed by pulse wave velocity (PWV). Statistical analysis was performed using one-way ANOVA. Ang II induced a similar level of hypertension in wt and ko mice and was not impacted by E or timing. In wt mice, PWV was significantly higher in Veh-treated compared with E-treated hypertensive animals, independent of timing (P<0.001). In contrast, PWV was not impacted by E in GPER ko mice (P=0.99). In conclusion, we found that E did not affect the hypertensive response to Ang II in both wt and GPER ko mice. GPER deletion reduced estrogen’s protection from arterial stiffening. Whether Ang II preceded or coincided with menopause did not alter the effects of E. These studies are important for determining whether cardiovascular status should be a factor when considering menopausal hormone therapy.