| Two experiments were carried out to evaluate the induction of metallothionein(MT) and the mediating function of corticosterone(CORT) in broiler chickens under heat stress by both acute heat stress and daily cyclic high temperature models, which may provide a theoretical basis for the future application of MT to alleviate poultry heat stress. This thesis was devoted to make the research from three respects as follows:1. Induction of MT in broiler chickens under acute heat stress and the mediation by CORTOne hundred ninety two 35-day-old healthy Arbor Acres(AA) male broiler chickens were assigned randomly to four treatments with 6 replicates of 8 chickens each: normal temperature(NT,23℃) group; normal temperature group by corticosterone intramuscular injection of 4mg/kg body weight(NT +CORT,23℃); high temperature(HT,35℃) group; high temperature group by the antiglucocorticoid RU486 hypodermic injection of 50mg/kg body weight (HT+RU486,35℃), of which NT group and HT group were injected by maize oil as comparison. The temperature was shifted from 23℃to 35℃and lasted for 3h. Samples were obtained, respectively, at 0h, 0.5h, 1h, 1.5h, 3h, 6h, 9h, 12h to evaluate the delicate changes of hepatic MT and the mediating function of plasma corticosterone. The results showed that acute heat stress induced significant changes of hepatic MT and MTmRNA: in comparison with the NT group, hepatic MT content was obviously decreased at 0.5h(P<0.05) in HT group and rised significantly at 1h, 1.5h as well as 3h time points(P<0.05),reaching the peak at 1.5h. While MTmRNA expression was markedly raised during the whole 3-h time(P<0.05) and showed the highest level at 3h time point. CORT injection under normal temperature induced significant increase of hepatic MT synthesis(P<0.05). In HT group, the tendency of hepatic MT and plasma corticosterone coined well with each other. While in HT+RU486 group, both hepatic MT and MTmRNA were remarkably decreased (P<0.05). The results suggested that hepatic MT can be significantly changed in broiler chickens under heat stress and the regulation of MT protein biosynthesis occurs primarily at the level of transcription.At the same time, corticosterone mediates the generation of hepatic MT in broiler chickens under acute heat stress.2. Induction of MT in broiler chickens under daily cyclic high temperature and the mediation by CORTOne hundred twenty 35-day-old healthy Arbor Acres(AA) male broiler chickens were randomly divided into four groups. Each group consisted of 6 replicates , and each replicate contained 5 chickens. The four groups are as follows: normal temperature group(NT, 23℃); high temperature(HT, 23-33-23℃) group, broilers of which were exposed to daily cyclic high temperature; Paired-Feeding group(PF,23℃) ,broilers of which were fed matching the diet intake of broilers in HT group at the previous day of the experiment; normal temperature with corticosterone supplement group(30mg/kg feed)(NT+CORT, 23℃). The experiment lasted for 7days and the samples were removed at 0d, 1d, 3d, 5d and 7d to investigate the general changes of MT under long-term daily cyclic high temperature and the mediating function of corticosterone. The results showed that both hepatic MT content and MT mRNA expression remarkably mounted up at 1d and 3d(P<0.05), and came down at 5d and 7d(P<0.05) in the HT group, perfectly inosculating with the tendency of plasma corticosterone, whereas, no significant changes were found in both NT and PF group(P>0.05). With CORT supplement, MT protein and MTmRNA expression were markedly increased in the NT+CORT group. The results suggested that significant changes of hepatic MT were mediated by corticosterone and had nothing to do with feed intake.3. Preliminary investigation of MT and SOD the on modulating time of heat stressBased on the model of acute heat stress and daily cyclic high temperature, investigation was carried out preliminarily to research the difference between MT and SOD on the modulating time of heat stress with SOD as reference object and malondialdehyde(MDA) as measurement of tissue oxidative damage, The results showed that, exposed to acute heat stress, hepatic MT was significantly increased at 1h and 1.5h, while hepatic SOD was insignificantly different at 1h and 1.5h(P>0.05), but it was dramatically increased at 3h and 6h(P<0.05); With glucocorticoid antagonist RU486 injected, hepatic MT protein was significantly decreased at 1h and 1.5h while SOD was significantly increased at 1h, 1.5h, 3h and 6h(P<0.05). Similar to the results of acute heat stress, hepatic MT of broiler chickens exposed to daily cyclic high temperature was significantly increased at 1d and 3d(P<0.05), while SOD was remarkably increased at 5d and 7d. These results suggested that it may be different for hepatic MT and SOD on the modulating time of heat stress.In conclusion, the results suggested that MT can be dramatically changed in broiler chickens under heat stress and the regulation of MT protein biosynthesis occurs primarily at the level of transcription. Corticosterone mediates the generation of MT. Moreover, it may be different for hepatic MT and SOD on the modulating time of heat stress. |
