| In order to study the effects of glucocorticoids on the protein metabolism of broiler chickens (Gallus gallus domesticus), exogenous glucocorticoids was used to induce stress on the early and later stage of broilers'development. mRNA level of several genes which were important for the protein metabolism were measured looking forward to constructing genetic regulatory networks of skeletal muscle protein metabolism as well as finding out its'detailed molecular mechanism.In trial 1, 48 male broilers (Arbor Acres) with similar body weight of 7 day were divided into 3 groups at random: DEX (Dexamethasone, hypodermic of abdomen on 8:00, 2.6mg/Kg·BW·Day), PF (pair-fed treatment that maintaining the same feed intake as DEX treatment. salt, hypodermic of abdomen on 8:00, 2.6mg/Kg·BW·Day), and NC (normal control group, salt, hypodermic of abdomen on 8:00, 2.6mg/Kg·BW·Day). After three days treatment, at 10 days of age, 8 birds with the mean body mass were randomly selected from each treatment; Blood was drawn from heart using a heparinized syringe after 12 hours fast. Plasma was obtained after centrifugation and was stored at ?20°C for further analysis. Immediately after the chickens were killed, the breast and thigh muscle tissues were dissected and weighed, about 2 g of left M. biceps femoris samples was sampled. The muscle samples were immediately cooled down in liquid nitrogen and stored at ?80°C until analysis. Thereafter, the muscle of right leg and whole breast were harvested and weighted respectively. The breast and thigh mass were expressed as percentage of body mass (%). After seven days treatment, at 14 days of age, the left 8 birds of each treatment were treated as above. The results indicate that the performance of birds suffered from stress were significantly lower. After three days treatment, birds of DEX show higher feed intake and lower mass gain, which makes the feed/weight ratio significantly higher. After seven days DEX exposure, birds of DEX show lower body weight and high feed/weight ratio. The breast yield (%) and thigh yield (%) were significantly higher after 3 days DEX exposure, but the absolute weight of breast muscle in two groups had no significant difference, the absolute weight of thigh muscle was lower after 3 days DEX exposure, and the breast yield (%) and thigh yield (%) were not altered by 7 days DEX exposure. The concentration of plasma uric acid (UA), total amino acid (T-AA) and insulin (INS) were higher at both sampling ages. The mRNA level of several genes that important for protein synthesis were significantly lower after three days exposure, while the mRNA level of genes that important for proteolysis were also lower. After three days DEX exposure, the activity of cationic amino acid transporter (CAT-2) on cell membrane was inhibited, the higher concentration of extracellular free amino acid can not reverse this situation. Myofibrillar protein breakdown in skeletal muscle progresses through two phases in response to chronic glucocorticoid administration, during the former phase proteolysis increased and protein synthesis decreased, followed by a later phase during which protein synthesis and proteolysis were likely to persist.In trial 2, 48 male broilers (Arbor Acres) with similar body weight of 35 day were divided into 3 groups at random: DEX (Dexamethasone, hypoderm- ic of abdomen on 8:00 and 18:00, 2.6mg/Kg·BW·Day), PF (pair-fed treatment that maintaining the same feed intake as DEX treatment. salt, hypodermic of abdomen on 8:00 and 18:00, 2.6mg/ Kg·BW·Day), and NC (normal control group, salt, hypodermic of abdomen on 8:00 and 18:00, 2.6mg/Kg·BW·Day), after three days DEX exposure, 16 birds of each treatment were divided into two groups: free access to feed and water(8 birds), and 12 hour fast only provided water (8 birds). Blood was drawn from a wing vein using a heparinized syringe. Plasma was obtained after centrifugation and was stored at ?20°C for further analysis. Immediately after the chickens were killed, about 2 g of left M. biceps femoris was sampled. The muscle samples were immediately cooled down in liquid nitrogen and stored at ?80°C until analysis. Thereafter, the muscle of right leg and whole breast were harvested and weighted respectively. The breast and thigh mass were expressed as percentage of body mass (%). Negative mass gain was observed after three days DEX exposure. But the breast yield (%) and thigh yield (%) were not altered by stress. The concentration of plasma glucose (GLU), UA, INS, IGF-I and T-AA were higher in DEX exposure treatment of normal feeding group. The high concentration of plasma GLU and INS indicate insulin resistance (IR), after three days DEX exposure only plasma UA, INS, T-AA concentration were higher in fasted group. Plasma IGF-I concentration was easily down regulated by 12 hours fast, and genes that important for protein synthesis were easily altered by fast or not during stress. |
