Comparison of lung injuries in pathological features and time-course changes between exertional and classic heatstroke rats

Objective To compare the differences in time-course changes and pathological morphology of lung injury between exertional and nonexertional heatstroke (HS) rats. Methods The rats were randomly (random number table) assigned into exertional heatstroke (EHS) group, nonexertional heatstroke (classic heatstroke, CHS) group, and two control groups (S-EHS and S-CHS respectively). The rats in the control groups were placed in a temperature of 23℃and humidity of (55±5)%, while the rats of EHS and CHS groups were exposed to ambient temperature of 39℃and humidity of 65%. During heat stress or sham heated, EHS and c-EHS rats underwent the exercise protocol which was performed by making rats running at a speed of 15m/min (without incline) for 8min, and then rest for 2min. Rectal temperature (Tr, HS), systolic blood pressure (SBP) and pulse rate (PR) were monitored to analyze the difference in heat stress response between EHS and CHS rats. The time point at which the SBP started drop down from the peak level was taken as a point of HS onset. At the onset of HS, heat exposure was terminated, and the rats were immediately removed from the chamber, and returned to room temperature. The rats were scarified at 0, 6, 24 and 72h after HS onset respectively, with 8 rats each time point. The lungs of all the animals were isolated for contrastive study on the differences of pathological changes of lung injury between EHS and CHS rats. Results In comparison with CHS rats, EHS rats had significantly shorten HS latency and smaller heat load to induce HS (P<0.01), while no difference was observed in Tr at HS onset between EHS and CHS rats (P>0.05). Pathological changes of acute lung injury could be observed in both CHS and EHS rats, which presented as progressive dilation and congestion of interstitial blood vessels, hemorrhage of alveolar space, abscission of alveolar epithelia cells and disappearance of alveolar tissue structure. Comparative study revealed that there was no significant difference in lung injury score between EHS and CHS rats at the onset of HS and 72h after HS onset, while lung injury score was significantly higher in EHS than in CHS rats (P