Cooling Treatment Induces Changes in Aquaporins Expression as a Protective Mechanism for Exertional Heat Stroke

Abstract

Xiuzhen Liu1, Bing Zhang1, Yuanlong Liu2, Liye Zou3. 1Tsinghua University, Beijing, China.2Western Michigan University, Michigan, MI.3The Chinese University of Hong Kong, Hong Kong, China. (Sponsor: Yuanlong Liu, FACSM) ABSTRACT: Cooling treatment is important to ensure the survival of patients with Exertional Heat Stroke(EHS); however, the protective mechanism of aquaporins in the cooling treatment of EHS is not very clear. Cooling treatment induces changes in renal aquaporins and regulates homeostasis of water metabolism,which mechanism involves aquaporin gene expression. PURPOSE: To determine the role of AQP2 mRNA expression and AQP2 protein expression in kidney in the homeostasis of water metabolism when EHS rats were treated with cooling. METHODS: In this study, there were 4 groups of male SD rats, including normal control group(NC,n=8), EHS onset group(EHSO,n=9), EHS rest group(EHSR n=9) and EHS cooling group(EHSC,n = 8). We established the rat model of EHS by exercising to exhaustion in the environment of 36°C temperature and 75% humidity until rectal temperature reaching about 42°C. The cooling treatment for EHS was to immerse in cold water for 5 minutes at 19°C. Blood and kidney were taken. Hct in serum was measured by automatic blood cell analyzer. PCR and WB were used to detect AQP2 mRNA expression and AQP2 protein expression respectively. Data were analyzed with Mann-Whitney U in nonparametric test. RESULTS: When EHS occurs, Hct increased significantly(EHSO: 0.43±0.29 vs. 0.40±0.04L/L,p<0.05). To fit for water metabolism, AQP2 mRNA expression and AQP2 protein expression were up-regulated significantly (EHSO vs. NC)(mRNA: 3.45±0.95 vs. 1.19±0.37, p<0.01; Protein: 2.76±1.01 vs. 1.00±0.00g/L, p<0.01). After cold water immersion, No significant change of Hct was found, AQP2 mRNA expression and AQP2 protein expression were significantly down-regulated(EHSC vs. EHSO)(mRNA: 1.66±0.33 vs. 3.45±0.95, p<0.01; Protein: 1.52±0.85 vs. 2.76±1.01g/L, p<0.05). CONCLUSIONS: Hct, AQP2 mRNA expression and AQP2 protein expression are pathophysiological biomarkers of EHS. Cooling treatment restrain water reabsorption by down-regulating the expression of AQP2 mRNA and AQP2 protein in kidney.