Effect of temperature on acute kidney injury in a rat model of renal ischemia‒reperfusion

Renal ischemia-reperfusion (I/R) injury is the main cause of acute kidney injury (AKI). A reliable and stable animal model is crucial for experimental research. Various factors affect the stability of animal models. In the present study, the effect of intraoperative temperature on the establishment of AKI model in rats, induced by I/R through bilateral renal pedicles clamping via the dorsal approach surgery, was investigated. Forty-eight male Sprague Dawley rats of 8-10 weeks were randomly divided into 6 groups (8 per group). The renal ischemia-reperfusion injury model was induced using a retroperitoneal double pedicle clamp procedure, using a clamping time of 50 min. The modeling procedure and sham operation were performed at different ambient air temperature, i.e., 15-20 °C, 20-25 °C and 25-30 °C. The general state of the rats, the ascites volume and mortality were observed after the operation. The serum creatinine (Scr) and urea nitrogen (BUN) levels of rats in each group were measured by an automatic biochemical analyzer 24 h post-operation. HE staining was used to observe pathological changes in renal tissues, and NF-κB p65 and interleukin-6 (IL-6) expression was measured by immunohistochemistry (IHC). TUNEL staining was used to assess apoptosis in renal tissues, and the expression of inflammatory markers, such as NF-κB and IL-6, and the apoptosis-related protein Bax was measured by Western blotting. There were no significant differences among the different sham operation groups. However, the abovementioned parameters were greater in the hypothermia, normothermia and hyperthermia model groups than in the corresponding sham operation groups, indicating successful model establishment. Scr and BUN levels were greater in the hyperthermia model group than in the other model groups, and there was obvious pathological damage to renal tissue. Notably, in the hypothermia model group, the general state of rats was good, Scr and BUN levels were not significantly increased 24 h post-operation, pathological damage to renal tissue and renal tubular epithelial cell apoptosis were mild, NF-κB and IL-6 protein expression was increased, and Bax protein expression was decreased. In conclusion, the induction of AKI by I/R at 20-25 °C has a high successful modeling rate and a low mortality rate. It may affect the stability of animal models by down-regulating the NF-κB/IL-6 signaling pathway and the NF-κB/Bax pathway through its anti-apoptotic and anti-inflammatory effects.