Recharacterizing the Murine Chronic Angiotensin II Infusion Model of Cardiovascular and Renal Injury

The chronic angiotensin II (AngII) infusion model is one of the most commonly used to study cardiovascular and kidney injury. However, the dosages of AngII used to induce cardiovascular or renal injury vary significantly in the literature. Therefore, we set out to determine the dosages of angiotensin II needed to produce renal injury and hypertension in mice. All experiments were performed in accordance with protocols approved by the Liberty University IACUC and conform to the FASEB standards for the use of animals in research and education. Male C57Bl/6J mice (~20 grams body weight) were purchased from The Jackson Laboratory and acclimated to our environment for one week. Mice were then assigned to receive 0, 400, 800, or 1200 ng AngII/kg BW*min for four weeks via osmotic minipumps (subcutaneous). Blood pressure (tail-cuff) was recorded each week of the study. At baseline, 2 and 4 weeks, renal blood flow and renal hemodynamics were estimated using contrast-enhanced ultrasonography. After 4 weeks, mice were placed in metabolic cages for the quantification of water intake and urinary output. Urine was stored for determination of albumin concentration using a commercially available ELISA. Mice were then euthanized and kidney tissues collected to measure the mRNA expression of several genes involved in the intrarenal renin-angiotensin system (RAS) (renin, angiotensinogen, angiotensin converting enzyme (ACE), ACE2, angiotensin II-receptor 1a (AT1a), and AT1b receptor) and tissue inflammation and remodeling [CCL5, α-smooth muscle actin (αSMA), collagen 1, collagen 3, and tumor growth factor β (TGFβ)]. All data were analyzed using general linear models in SPSS. Mice administered the 800 dose had the greatest and most consistent increase in systolic blood pressure (147 ± 8mmHg) as compared to mice administered the saline (114 ± 9, P=0.004) and the 400 dose (121 ± 11mmHg, P=0.01). Mice administered the 1200 dose tended (P=0.08) to have a greater total renal blood flow throughout the study, with a significant increase (P=0.047) in cortical blood flow as compared to mice administered saline. Despite the modest changes in estimated renal blood flow, mice administered the 800 and 1200 doses of AngII had similar, yet significantly greater (P≤0.001) water intake and urinary output as compared to mice treated with saline or the 400 dose. Similarly, mice with the 800 and 1200 doses had significantly greater evidence of tissue damage evident by increased albuminuria (P≤0.05) and increased renal gene expression of CCL5, TGFβ, collagen 1, and collagen 3. There was also an effect on the intrarenal RAS, with mice administered the 800 and 1200 doses having significant (