Effects Of Stress On Glucose Metabolism Of Skeletal Muscles In Broilers And The Underlying Mechanism

Several trials were conducted to investigate the effects of stress on glucose metabolism in skeletal muscles of broilers and study the underlying mechanism. We used exogenous glucocorticoids to induce stress and studied the individual and associative effects of glucocorticoids, insulin and nitric oxide (NO) on glucose metabolism in skeletal muscles of broilers via in vivo and in vitro experiments.The part 1 of chapter 2 included two small experiments. One was chronic stress treatment and the other was actute stress treatment. In part 2 of chapter 2, the M. fibularis longus muscles of thirty-six broilers were incubated in vitro to measure the basal or insulin-induced 2-deoxyglucose (2-DG) transport rate combined with the NO donor sodium nitroprusside (SNP) (10 mM/l), or NO synthase (NOS) inhibitor NG-nitro-L-Arginine methyl ester (L-NAME) (2 mM/l) with a double isotopes label method, in order to investigate the effects of extrinsic administration of corticosterone (CORT) on glucose intake in skeletal muscles of broilers. The design of part 3 was almost the same as the part 2, except that the administration of CORT in this trial was in vivo (4 mg/kg). After the incubation of these muscle samples, the 2-DG transport rate, the concentration of NO, the activity of NOS and the level of glycogen were determined. The results indicated that SNP increased the basal or insulin-stimulated 2-DG transport rate of these muscles, which was a hint that NO was a critical mediator in mechanism of glucose metabolism. It was likely that the increased 2-DG transport in basal muscle by a pharmacologically high dose of CORT revolved in the elevation of glycogen content, but this could not confirm that CORT promoted the effective use of glucose. The 2-DG transport rate stimulated by insulin was reduced when the muscle was treated with CORT, but the capacity of glucose intake was improved when SNP added. We inferred that acute stress in broilers could cause their levels of NO declined first, which correlated with their IR by glucocorticoid to a certain extent. In contrast to the effects of NOS inhibition in vivo, L-NAME failed to affect basal or insulin-stimulated 2-DG transport in isolated muscles incubatd using in vitro preparations; this suggested that hemodynamic factors were needed to fully amplify the increase in basal or insulin-stimulated glucose transport in skeletal muscles.There were 3 trials in chapter 3, which adopted a IR model of broilers mimicked by CORT administration and combined the glucose load experiment with L-arginine load experiment. In each trial 24 broilers with uniform weights were divided into GLU, L-ARG, GLU+L-ARG and control group randomly. All the broilers were fasted at first. 6 hours later, using the same dose (0.4 ml/kg BW), the broilers in trial 1, 2, 3 were injected hypodermically with saline and corn oil, CORT (dissolved in the corn oil, 10 mg/ml) and saline, insulin (dissolved in the saline, 2.5 IU/ml) and corn oil respectively. Then delivered by intubation in the crop, the broilers in GLU, L-ARG, GLU+L-ARG and control group were administered a glucose load of 2g per kg BW, a L-arginine load of 0.5g per kg BW, a glucose combined with a L-arginine load and a distilled water load of 5ml per kg BW respectively. Just before and 30, 60, and 120 min after these loads, a blood sample was taken from a wing vein using a syringe and was transferred to iced tubes. After centrifugation at 4°C, plasma was frozen until assayed. The concentration of plasma glucose, insulin, NO, NOS, uric acid and triglyceride were determined. The results indicated that the massive release of glucocorticoids induced IR, which correlated with the vascular endothelial dysfunction by glucocorticoids and hence the reduction of NO concentration in bodies in a way. As for the research on the L-arginine as a NO donor, there are many contradictory conclusions between animal experiments and clinical trials. However, we truly observed the promotive effects of L-arginine on the production of NO. L-arginine can be applied as an effective NO donor to the animal production and clinical therapy. The stress negatively influenced the proteins, lipids and carbohydrate metabolism of broilers while the L-arginine could regulate the vascular endothelial dysfunction, modulate the metabolic disorder and reduce the passive influence of stress to some extent. NO had something to do with insulin, which might have a series of beneficial influence on the maintenance of normal function of insulin, such as improving the sensitivity of insulin, preventing IR and so on. When the concentration of plasma glucose was at a normal level, the increase of L-arginine in blood only had a trivial effect on the release of insulin. However, under the circumstance of hyperglycemia, excessive L-arginine could cause the release of insulin to increase by several times.