Thermoregulation and antioxidant defense mechanisms in Eurasian tree sparrows (Passer montanus) under acute heat stress

Global warming has become an undeniable fact, and the frequent occurrence of extremely hot weather is a serious challenge to the survival of animals. As one of the most active components of the ecosystem, birds are sensitive to the constant changes in the climate and environment. To investigate the physiological responses of Eurasian tree sparrows (Passer montanus) to acute heat stress, various thermogenic parameters of the birds, which included resting metabolic rate (RMR), body mass, body temperature, water intake, and liver cellular metabolic capacity, were measured after exposure to 42 degrees C for different times. The antioxidant response of Eurasian tree sparrows to heat stress was investigated by measuring the lipid oxidation indexes and related antioxidant oxidase activities in the serum and liver. Body temperature and water intake were significantly increased after 2 h of heat stress and lasted until the end of the heat stress (12 h). In contrast, RMR was significantly decreased after 2 h of heat stress. At the cellular level, liver COX activity was significantly increased during heat stress from 2 h to 6 h. Additionally, there was a significant increase in MDA content and superoxide dismutase (SOD) and catalase (CAT) activity levels in the serum. The glutathione peroxidase (GSH-PX) activity in the liver was significantly decreased after 2 h of heat stress. Our results indicated that heat production decreased while heat dissipation increased in Eurasian tree sparrows exposed to acute heat stress. At the same time, the internal antioxidant defense system of the birds was activated to counteract the damage caused by high temperatures. Therefore, it was reasonable to speculate that Eurasian tree sparrows might be resistant to high temperatures to the extent that they can maintain normal life activities through the regulation of thermogenic and antioxidant systems under acute heat stress.