Effects Of Water Immersion On Lung Tissue Injury And Prognosis In Rats During The Early Stage Of Heat Stress Recovery

Objective To investigate the effects of temperate-water immersion and ice water immersion cooling treatments on lung histopathology, the related cytokines in lungs and the constituent ratio of death in rats during the early stage of heat stress recovery to find out the roles of water immersion cooling treatments on lung tissue injury induced by heat stress.Methods In the first part of our study, the heat stressed(HS) rats were immediately cooled via room temperature(22.0??24.0?), temperate-water immersion(TWI,20.0??22.0?) and ice water immersion(IWI,2.0??4.0?), respectively. Forty five male SD rats were randomly divided into three groups: HS(n=15), HS+TWI(n=15), HS+IWI(n=15). The constituent ratio of death in each group was calculated 3 hours after HS.In the second part of our study, forty nine male SD rats were randomly divided into four groups:normothermic control (NC, n=7), HS(n=14), HS+TWI (n=14), HS+IWI(n=14). Rats in the NC group were exposed to room temperature(22.0??24.0?). Rats in the other three groups, after being heated, were immediately cooled via room temperature(22.0??24.0?), temperate-water immersion(TWI,20.0??22.0?) and ice water immersion(IWI, 2.0??4.0?) respectively. Sacrifice these rats 15 minutes or 3 hours after heat stress respectively, named as HS+15min(n=7), HS+3h(n=7), HS+TWI+15min(n=7), HS+TWI+3h(n=7), HS+IWI+15min(n=7), HS+IWI+3h(n=7). We then (1) motored the core temperature (Tc) and calculated the cooling rates; (2) performed hematoxylin and eosin staining to evaluate lung tissue injury and lung tissue injury scores; (3) performed enzyme-linked immunosorbent assay to detect the levels of tumor necrosis factor-alpha(TNF-?)? interleukin-6(IL-6)?interleukin-10(IL-10)?transforming growth factor beta1(TGF-?1)?vascular endothelial growth factor a(VEGF-A) of the lung homogenate and analyzed the correlation between the level of VEGF-A and TGF-?1, TNF-?, IL-6, respectively.Results In the first part of our study, compared with the HS group, the constituent ratio of death in the HS+TWI group and the HS+IWI group decreased significantly.In the second part of our study, (1) the cooling rate of the HS+IWI group was faster than that of the HS+TWI group, compared with which the cooling rate of the HS group was slower. (2) In the HS+3h group, the Tc at three hours after HS was lower than that before HS(P=0.015), while no such decreases were found in the HS+TWI+3h group and the HS+IWI+3h group. (3) Rats in the HS+IWI+3h group displayed alveolar collapse, edema, hemorrhage and thickened interstitium, and higher levels of the inflamatory cytokines TNF-? and IL-10, as well as VEGF-A, compared with rats in the NC group and the HS+3h group. (4) The level of VEGF-A increased notably above the baseline 15 minutes after heat stress and decreased notably under the baseline 3 hours after heat stress, and performed significant correlation with the level of TGF-?1, but none with TNF-? or IL-6.Conclusion TWI and IWI can accelerate the cooling rate, prevent hypothermia and improve the prognosis during the early stage of heat stress recovery, while IWI may aggravate the pulmonary inflammation and cause lung tissue injury which suggests that IWI may not be the best cooling treatment for its side effect. The noticeable change of VEGF-A was only correlated with TGF-?1, independent of the related inflamatory cytokines, which suggests VEGF-A may play crucial role in the lung tissue injury during the early stage of heat stress recovery.