Time of day of CXCR2 stimulation drives Ang II-induced hypertension

Continuous infusion of Ang II initiated during the mouse inactive period is routinely used as a model of hypertension pathogenesis, leading to the identification of the immune system in the development of this disease. Recently our lab demonstrated that the blood pressure response to Ang II is time-of-day dependent wherein initiating continuous infusion of 490 ng/kg*min Ang II during the onset of the active period at zeitgeber time, ZT12-14, resulted in significantly lower blood pressure than when infusion begins during the onset of the inactive period, ZT0-2 (Day 7 24-hr mean arterial pressure, 117±12 mmHg or 135±11 mmHg, respectively, n=8/group, P< 0.01). These unique blood pressure responses moderated by time of initiation of Ang II infusion suggest that the immune response in the first 12-hours are critical to the hypertensive phenotype. We first assigned mice to receive continuous vehicle or Ang II infusion (490 ng/kg*min, osmotic minipump, Alzet) initiated at ZT 0-2 or at ZT 12-14. To identify whether there is an initial difference in cytokine response, plasma was obtained via cardiac puncture after 12 hours for cytokine analysis (Luminex MCYTOMAG-70K-PX32). Initiating Ang II at ZT 0 but not ZT 12 resulted in a 10-fold elevation of plasma G-CSF compared to time-matched controls (1766±398 pg/mL vs 156±23 pg/mL, n=4-5/group, p< 0.0001). Likewise, CXCL1/KC (346±107 pg/mL vs 49.7±9 pg/mL, p = 0.0102) and IL-6 (64.4±13 pg/mL vs 7.2±0.7 pg/mL, p = 0.001) were only significantly elevated above their time matched controls when Ang II infusion began at ZT 0 (Two-way ANOVA, n = 4-5/group). Surprisingly, IL-2 (8.8±1.5 pg/mL vs 4.7±0.3 pg/mL, p = 0.0162, Two-way ANOVA, n = 5/group) was significantly elevated above its time-matched control when Ang II infusion began at ZT 12 but not ZT 0, suggesting distinct innate and adaptive immune responses occurring within 12 hours of infusion initiation. G-CSF promotes CXCR2-mediated neutrophil activation and CXCL1 is the ligand for CXCR2, thus we hypothesized that acute CXCR2 antagonism at the time of Ang II infusion would mitigate the hypertensive phenotype. To test this hypothesis, we co-administered a single bolus of the competitive CXCR2 antagonist SB 225002 (Sigma-Aldrich, 0.3 mg/kg, i.p.) in mice also receiving implantation of the osmotic minipump to initiate continuous infusion of Ang II at ZT 0. Co-administration of a single dose of the CXCR2 antagonist significantly attenuated blood pressure elevation to Ang II compared to vehicle for 7 days after infusion initiation (Day 7 24-hr mean arterial pressure, 109±8 mmHg vs. 138±9 mmHg, n=5-8/group, P< 0.01). These findings demonstrate that acutely blocking the CXCR2 signaling pathway at the onset of Ang II infusion at ZT0-2 is sufficient to blunt the longer-term hypertensive response. Future research is needed to clarify how the time of day of Ang II-induced immune activation modifies end-organ damage and blood pressure responses.Acknowledgments: NIH KUH PRIME TL1 DK139566 AHAPOST1377428 (LNB), NIH R01 DK134562 (DMP&JSP). This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.