Angiotensin II-Induced Hypertension is Time-of-Day Dependent

Angiotensin (Ang) II-induced hypertension is a common model of hypertension that entails infusing Ang II in rodents beginning during the inactive (lights-on) period. Using this model, investigators found that the immune system, particularly activated T cells, plays an instrumental role in the pathogenesis of hypertension. T cells exhibit time-of-day differences in activation capacity, cell fate, and tissue migration. However, it is unknown whether Ang II-induced hypertension is time-of-day dependent. Thus, we hypothesized that the blood pressure and T cell responses to Ang II infusion are dependent on the time-of-day. Male C57BL/6J mice were randomly implanted with telemetry (DSI, C10) at 9 weeks of age to monitor blood pressure (BP). After 2 weeks recovery, mice were then assigned to receive vehicle or continuous Ang II infusion (490 ng/kg*min, osmotic minipump, Alzet) initiated during the light, inactive period (zeitgeber time (ZT) 0-2) or during the dark, active period (ZT 12-14, minipump implanted under red light). In a separate set of mice, kidneys were dissected for IHC, peripheral blood T cells (PBTs) were harvested (Invitrogen 11443D) for bulk RNA sequencing (Azenta) after 7 days of vehicle or Ang II infusion, and PBTs were harvested on day 14 for assaying T cell activation capacity. Initiation of Ang II infusion at ZT 12-14 resulted in significantly lower systolic blood pressure response compared to initiation of Ang II infusion at ZT 0-2 (p<0.01, n=8/group, Day 7 24-hr BP = 117±11.65 or 135±11.17 mmHg [±SD], respectively). To address the potential time-of-surgery confounder, we implanted programmable peristaltic minipumps (iPrecio) at ZT 0-2 and delayed Ang II infusion by 30 or 42 hours while monitoring BP via telemetry. The interaction between timing of Ang II initiation and blood pressure was independent of time-of-surgery (P=0.0235, n=3/group). There was reduced CD3 + T cell accumulation (p<0.05, n=20,19) on day 7 in the kidneys of mice with Ang II infusion initiated at ZT 12-14 compared to ZT 0-2. BulkRNA sequencing of PBTs led to the identification of 1429 genes (adj.p<0.05) that were significantly different based on the time-of-day irrespective of Ang II infusion, while 233 genes (adj.p<0.05) were differentially expressed based on the time of initiation of Ang II infusion. Initiation of Ang II infusion at ZT 12-14 resulted in attenuated peripheral blood CD8 + IFNγ and IL-17a (P < 0.05, n=6/group) production capacity on day 14 compared to ZT 0-2 infusion. These findings demonstrate that BP and T cell responses to exogenous Ang II infusion are time-of-day dependent. Furthermore, these data indicate that mechanistic studies in rodent models need to consider the time of day when modeling hypertension. NIH KUH PRIME U2C DK133422 TL1 DK139566 (LNB), NIH R01 DK134562 (DMP&JSP). This abstract was presented at the American Physiology Summit 2025 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.