Central And Peripheral Mechanisms Underlying The Growth Promoting Effect Of Cysteamine In Broiler Chickens

To gain more insights into the mechanisms of cysteamine's growth promoting effects in broiler chickens, the present study determined the accompanied changes of serum levels of some metabolic hormones and mRNA expression of genes in somatotropic axis and gastrointestinal tract, after diet supplementation or gastric perfusion of cysteamine in broiler chickens. At the same time, antioxidant effect of cysteamine was observed.1. Effect of cysteamine on expression of genes in somatotropic axis1) Diet supplementation of cysteamine on somatotropic axis gene expression22-day-old AA broilers were supplemented with 400mg/kg cysteamine hydrochloride compound in their basal diet for 21 days. Body weight, the rate of breast muscle, the rate of leg muscle were recorded at slaughtering and the SS, GH, GHR mRNA expression levels were determined. The results showed that:Compared to the control, body weight in cysteamine-treated group was increased significantly (P<0.01,n=100), the rate of the breast muscle increased significantly (P<0.01,n=100), while no difference was found in the rate of the leg muscle.No significant difference was found in serum T3 concentration, but serum T4 concentration reduced significantly (P<0.05, n=40).The relative abundance of hypothalamic SS mRNA was reduced significantly (P<0.05, n=32), which was accompanied with a marked increase in pituitary GH mRNA (P<0.05, n=32). However, no significant difference was found in hepatic GHR mRNA expression.Both in control and in cysteamine-treated groups, the relative abundances of breastmuscle GHR mRNA was significantly higher than that of leg muscle (P<0.01,n=32). 2) Gastric perfusion of cysteamine on somatotropic axis gene expression47-day-old AA broilers were perfused daily with 70 mg of cysteamine hydrochloride compound for 3 or 6 days. The results showed that:No differences were found in the serum T3 and T4 concentrations after 3 and 6 days of perfusion.No differences were found in the expression of hypothalamic SS mRNA after 3 and 6 days of perfusion.2. Effect of cysteamine on expression of genes in gastrointestinal tract1) Diet supplementation of cysteamine on exression of gastrointestinal genesNo difference was found in serum insulin concentration whereas serum glucagon concentration increased significantly (P<0.05, n=40).No differences were found in the relative abundance of proventricular SS mRNA and duodenal SS mRNA.2) Gastric perfusion of cysteamine on genes involved in digestion and absorptionNo differences were found in serum insulin and glucagon concentrations after 3 days of cysteamine perfusion. No difference was found hi serum insulin concentration after 6 days of perfusion, but serum glucagon concentration increased significantly (P<0.05, n=20).No differences were found in the relative abundance of hypothalamic ghrelin mRNA after 3 and 6 days of perfusion.No differences were found in the relative abundances of proventricular SS and ghrelin mRNA after 3 and 6 days of perfusion.The relative abundances of duodenal SS mRNA reduced significantly after 3 and 6 days of cysteamine perfusion (P<0.05, n=16), but no differences were found in the expression of ghrelin mRNA and SGLT1. The relative abundance of duodenal GLUT2 mRNA reduced significantly after 3 days of perfusion, but no difference was found after 6days of perfusion.The activity of duodenal protease increased significantly after 3 days of perfusion, but no difference was found after 6 days of perfusion.3. Effect of cysteamine on scavenging of free radicalsNo differences were found in serum SOD and MDA concentrations after diet supplementation of cysteamine.No differences were found in SOD concentration of duodenal homogenate after 3 and 6 days of cysteamine perfusion. The MDA concentration of duodenal homogenate reduced significantly after 3 days of perfusion (P<0.05, n=20), but no difference was found after 6 days of cysteamine perfusion.