Anesthetic Influences Outcomes of the Chronic Angiotensin II Infusion Model in Mice
Medicine and Health Sciences
The chronic angiotensin-II (AngII) infusion model is commonly used to study kidney and cardiovascular injury, however the methodologies used to generate the model varies significantly in the literature. Published doses range from 100 to 3000 ng/kg*min with a wide range of blood pressure and other outcomes measured. Interestingly, there is a variety of anesthetic agents used to implant the miniosmotic pumps that deliver the AngII. While the anesthetic exposure is brief, and the anticipated physiological effects of are expected to have worn off within hours to days after administration, data in other animal models of kidney disease suggest that anesthetic influences the inflammatory response and subsequent physiological outcomes. Therefore, we set out to determine if blood pressure, renal function, or markers of kidney inflammation are affected by the anesthetic used to implant the miniosmotic pumps. 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/6 mice (~20 grams) were purchased from The Jackson Laboratory and acclimated to the Liberty University vivarium for 7 days. Mice were then randomly assigned to receive miniosmotic pumps (Alzet, model 2004) delivering 500 ng/kg*min AngII (subcutaneous) using either 1) 3% isoflurane inhaled (in oxygen, ISO), 2) a ketamine/xylazine mixture) (KX) 90 and 9mg/kg intraperitoneal injection, respectively), or 3) a 2.5% tribromoethanol solution (TBE, 240mg/kg intraperitoneal injection). The tribromoethanol solution was prepared, stored and administered based on policies published by several different academic institutions. Blood pressure measurements began 3 days after pump implantation and continued for 4 weeks using the non-invasive tail-cuff method. At weeks 2 and 4, mice were placed in metabolic cages to assess water balance and collect urine to quantify albumin excretion. After 4 weeks, renal resistive index (renal segmental arteries) was determined for each mouse by ultrasound. Mice were then euthanized and the heart was weighed to assess for cardiac hypertrophy. Kidney tissues were also collected for quantification of inflammatory gene expression [interleukin-6 (IL6), IL1β, CCL5, and tumor growth factor β (TGFβ)] using real-time PCR. All data were analyzed using general linear models in SPSS. Neither AngII nor anesthetic caused a significant increase in systolic blood pressure (P=0.8) or heart weight (P=0.4). However, there was a significant effect of anesthetic on water intake and urinary output at weeks 2 and 4, with mice of the KX group consuming less water and producing less urine (P<0.05) than mice of the ISO or TBE groups. Interestingly, the TBE had 2–3 times greater (-P=0.03) urinary albumin excretion and renal mRNA expression of CCL5 and TGFβ (P<0.04). Taken together, our data suggests that the choice of anesthetic used to implant the miniosmotic pump significantly influences outcomes of kidney health in the chronic AngII-infusion model. More studies are needed to better characterize this valuable animal model and increase the reproducibility across different laboratories and institutions.
Damir Pogarcic, Kelsie M. Smith, Riley M. Lutz, and Joseph C. Gigliotti, Anesthetic influences outcomes of the chronic angiotensin II infusion model in mice, The FASEB Journal, Volume 33, Supplemental Issue 1, April 2019, https://www.fasebj.org/doi/abs/10.1096/fasebj.2019.33.1_supplement.lb540