Effects Of Glucocorticoids On The Mechanisms Of Feed Intake In Broilers

To investigate the effects and mechanisms of glucocorticoids on the mammalian target of rapamycin (mTOR) appetite and energy pathway of broilers (Gallus gallus domesticus), exogenous glucocorticoids was used to mimick stress on two phases of stress development of broilers. Changes of Protein and mRNA expression level of important genes in appetite regulation and mTOR pathway in hypothalamus were measured and analyzed, in order to providing countermeasures for reforming energy waste in broiler chicken production. In experiment 1, there were two similar trails. In trial 1, 80 male AA broilers were divided into two groups: glucocorticoids and control. Each group had 10 repetitions and each repetition had 4 broilers. Broilers were injected with the same dose of dexamethasone(DEX) and saline at 6:00 (11d-13d), respectively. At the day of 13, samples (blood and hypothalamus) were obtained at 8:00 and 9:00. In trial 2, group dividing and the treatment were the same as which in trail 1, except that the time of injection was 10:00, and samples were obtained at 12:00. The results showed that the glucocorticoids had no significant effect on the relative expression of mTOR pathway-related genes at 8:00(before foodintake). After refeeding 1h, glucocorticoids significantly increased the relative expression of PI3Cα, and tend to increase the relative expression of PI3Cβand EEF2. But no sinificant effect on the other factors. Compared with control treatment, the mRNA level of mTOR pathway-related genes were no significant changes in trial 2.In experiment 2, 48 male AA broilers with similar body weight were divided into 4 groups randomly, there were 6 repetitions in every group with 2 broilers in every repetition, rearing in separate cage. In group 1, male AA broilers were subcutaneous injected with DEX (2.6 mg/kg BW) at 6:00 from 11 to 13 days old ,and diets were high energy (ME, 3.6kcal/kg; CP, 20%), Group 2 is control group, Saline was injected with a suitable dose ,and diets were high energy, treats were the same as in group 1 except that dexamethasone was displaced by saline. Group 3 animals were injected by DEX and diets were low energy(ME, 2.6kcal/kg; CP, 20%), in group 4, animals were injected by saline, and diets were low energy. At the day of 13, samples (blood and hypothalamus) were obtained at 8:00 and 9:00 (GroupA and B were feed by high energy food, and Group C and D were feed by the same quality low energy food with Group A and B). The results showed that glucocorticoids had no significant effect on the relative expression of NPY, GR, INSR, AKT3, 4EBP1, mTOR, AgRP, POMC before and after ingestion in the stage of low energy diets. The glucocorticoids tend to reduce relative expression of GR, and tend to increase the relative expression of AgRP, in the low energy diet groups. In the stage of high energy diets, the glucocorticoids increased the relative expression of INSR, AKT3, 4EBP1(P<0.05), and the relative expression of POMC trend to decrease. All the effects vanished after refeed. there was no significant effect of glucocorticoids on relative expression of NPY, GR, mTOR, AgRP before and after ingestion in the stage of high energy diets.In part 2, The broilers were randomly assigned to 6 group, 8 birds per group. After 21h fasting at 6:00, three groups (A, B, C) were injected by DEX in a dose of 2.6 mg/kg.BW, and another three group(A', B', C') were treated with same dose saline. At the day of 11, blood and hypothalamus of Group A and A'were obtained at 9:00, at the same time the animals of Group B and B'were feed by high energy diets, the animals of Group C and C'were feed by low energy diets. At 10:00 all the blood samples were obtained, and hypothalamus were quick-freezed in liquid nitrogen. The results showed that glucocorticoids had no significant effect on the relative expression of AgRP, NPY, POMC, GR, Ghrelin, MC4R, INSR after fasting for 24h. The glucocorticoids significant increased the relative expression of NPY(P<0.01), and no significant changes of AgRP, POMC, GR, Ghrelin, MC4R, INSR were found. In the DEX-treated group the relative expression of NPY trend to increase at the stage of 1h refeeding of low energy diets, and there were no significant changes of the relative expression of AgRP, POMC, GR, Ghrelin, MC4R, INSR.