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Background: Activation of the sympathetic nervous system causes vasoconstriction and an acute reduction in peripheral blood flow. However, during hypoxia, sympathetically-mediated vasoconstriction is attenuated in young females without obesity. Given sustained increases in sympathetic activity associated with obesity may create a greater propensity to vasoconstrict in response to sympathetic activation, we sought to examine the effect of obesity on the vascular response to sympathetic activation during hypoxia. We hypothesized sympathetically-mediated vasoconstriction during hypoxia would be greater in premenopausal female adults with obesity when compared to females without obesity. Methods: Blood pressure (BP, finger photoplethysmography) and forearm blood flow (FBF, venous occlusion plethysmography) were assessed in premenopausal female adults with obesity (n=5, 25±3 yrs, 37±1 kg/m2, 48±1% body fat) and without obesity [n=19, 23±1 yrs, 23±1 kg/m2, (33±2% body fat, n=8)]. Data were combined from two cohorts (IRB #2022525, 2011312) to test present hypotheses. Participants completed two trials consisting of a 2-min cold pressor test (CPT) during baseline normoxia (98±1% SpO2) and following 3-5 min of steady-state hypoxia (0.10±0.01 FiO2, 82±1% SpO2). FBF was normalized for BP (forearm vascular conductance, FVC) and a change in FVC during the last 1-min of CPT was calculated (ΔFVC). The main effect of group (obese, non-obese), condition (normoxia, hypoxia) and the interaction of group and condition were compared using a two-way repeated measures ANOVA. Results: In female participants without obesity, ΔFVC during normoxia was attenuated during hypoxia (-0.57±0.19 vs +0.36±0.34 mL/dL/100mmHg/min; p=0.009). Conversely, in female participants with obesity, ΔFVC during normoxia did not differ from the response during hypoxia (-0.31±0.46 vs -0.87±0.34 mL/dL/100mmHg/min; p=0.382). Group differences in ΔFVC were not observed during normoxia (p=0.657), but were present during hypoxia (p=0.039). Conclusion: Sympathetically-mediated vasoconstriction is attenuated during steady-state hypoxia in premenopausal females without obesity, whereas this response is not observed in female adults with obesity. These preliminary data advance our understanding of the impact of obesity on hypoxic vascular control in premenopausal female participants and have implications for conditions in which hypoxia and sympathetic activation are observed ( e.g., sleep apnea, heart failure, COVID-19). NIH HL130339 (JKL), NIH HL153523 (JKL), AHA 909014 (DWJ) This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.