| Heat stress had negative effects on animal growth performance and reproductive ability. It decreased feed intake, increased the occurrence of disease frequency and the consumption of nutrition metabolism of animal, which lead to poor growth of animal and great economic losses in livestock industry. It has obtained widespread attention of scholars from various countries that adopting nutrition regulation method to alleviate the negative effects induced by heat stress.The present study investigated the antioxidant function in liver of mice on the model of heat stress, and study the relative mRNA expression levels of Keap1-Nrf2/ARE signal pathway. On the other hand, we added TBHQ to the diet of mice to study whether it can improve the ability of anti-heat stress.Experiment one: Effects of heat stress on antioxidant function in liver of mice. Thirty8-weeks old male mice were chosen. Mice were housed under controlled conditions (42℃,60%RH) for2hours (between11:00and13:00) for twelve consecutive days. Five mice from each goup were sacrificed after heat treatment, liver samples were collected. The results showed: The body surface temperature and rectal temperature markedly increased after heat treatment to before heat treatment (P<0.01). On the first and second days after heat treatment, liver organ index significant increased to the control (P<0.01). Heat stress also lead to the hyperemia and cellular edema in liver. These results showed that heat treatment lead to damages in liver of mice. On the second and eighth days after heat treatment, hepatic MDA content significant increased to the control. On the fourth and twelfth days after heat treatment, GSH content, GSH-PX activity and T-SOD activity increased to the control. Antioxidant system and oxidant system interact with each other. In contrast to the control, Keapl mRNA expression decreased significantly from the first day; Nrf2mRNA expression increased significantly on the fourth and twelfth days; HO-1mRNA expression increased significantly on the first day; NQO1and GCLC mRNA expression increased significantly on the first and fourth days; Nrf2protein was detected in cytoplasm of hepatic cell on the first, second, fourth and eighth days. Relative mRNA expression of Keapl-Nrf2/ARE signal pathway were activated. Antioxidant system start to regulate the oxidant damages by heat stress in liver.Experiment two: Attenuating effects of TBHQ diets on oxidant damages in liver of heat stressed mice. Thirty-five6-weeks old male mice randomly assorted into2groups (Basic group, TBHQ group). Basic group was provided basal diets, and TBHQ group was provided1%TBHQ diets. Mice were taken heat treatment after2weeks. The method was as same as experiment one. The results showed:On the first day after heat stress, liver organ index of mice significant increased to before heat stress(P<0.01). On the second, fourth and eighth days after heat stress, there were no significant changes in hepatic morphology after heat stress to before heat stress. Taken the results of experiment one together, it showed that TBHQ diets had a protective effect on the liver of mice. Two weeks after breeding different type diets, the hepatic GSH-PX activity and T-SOD activity significant increased, Keapl mRNA expression decreased in TBHQ group in contrast to basic group. These results showed that TBHQ diets increased the antioxidant levels in liver of mice. In contrast to the control, On the first, fourth and eighth days after heat stress, hepatic MDA content markedly increased; On the second day after heat stress, hepatic GSH content markedly increased; On the first, second and fourth days after heat stress, hepatic GSH-PX activity markedly increased; Keapl mRNA expression increased significantly on the fourth and eighth days; Nrf2mRNA expression increased significantly on the first and eighth days; HO-1mRNA expression increased significantly on the first and fourth days; NQO1mRNA expression increased significantly on the first, second and eighth days; GCLC mRNA expression increased significantly on the first day. Nrf2protein was detected in cytoplasm of hepatic cell at the first, second and fourth day. These results showed that relative mRNA expression of Keapl-Nrf2/ARE signal pathway were activated quickly.In summary, administration of TBHQ increased the antioxidant levels in liver and decreased the oxidative damages to liver induced by heat stress. We suggested that TBHQ took effects by activating the relative mRNA expression of Keapl-Nrf2/ARE signal pathway. |
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