Effects Of Feed Restriction And Insulin Treatment On Adiponectin And Lipid Metabolism In Broilers

Adiponectin?ADPN?is a protein synthesized and secreted predominantly by adipocytes into the peripheral blood.Circulating ADPN levels are inversely related with several diseases and its functions predominantly in conditions including insulin sensitivity,anti-diabetic,anti-inflammatory and anti-atherosclerosis.ADPN is closely related to fatty acid synthesis and oxidation.Different energy status may affect ADPN secretion and lipid metabolism in broilers.In this study,the secretion of ADPN in organs with a high lipid metabolism was determined by assessing the temporal and spatial expressions of ADPN,and thereafter,two models of energy status?feed restriction and insulin treatment?were established to study the response of ADPN and lipid metabolism to energy status,and to determine the relationship between ADPN and lipid metabolism.The results of this study are helpful for the establishment of breeding and control techniques for poultry,and provide a basis for the improvement of poultry production and poultry performance.Experiment 1 Spatial and temporal expressions of ADPN in broilersSpatial expression:We analyzed the mRNA expressions of ADPN and its receptors in different tissues of 42 days old broilers.The results showed that the mRNA expression of ADPN and its receptors were highest in abdominal fat,followed by duodenum,glandular stomach,heart and hypothalamus,also in lipid-metabolically active tissues including liver and muscles tissues?P<0.0001?.Temporal expression:We analyzed the mRNA expression of ADPN and its receptors in different tissues of broilers at different embryonic days?11E,13E,15E,17E,19E?and weeks of age?18E,0W,1W,2W,3W,4W,5W and 6W?.The results showed that the abdominal fat rate increased significantly,while the plasma ADPN concentration increased significantly during broilers growth.Linear regression analysis showed that there was a positive correlation between ADPN in plasma and abdominal fat rate in broilers?r=0.5799;P<0.0001?,but it was opposite correlated with very low density lipoprotein?VLDL?.The mRNA expressions of ADPN in the liver?P<0.0001?,breast?P=0.0011?and thigh?P<0.0001?muscles of broilers were significantly increased with increasing embryonic age.The mRNA expression levels of ADPN and its receptors in abdominal fat were increased with the growth of broilers.The mRNA expression levels of ADPN and its receptors in other tissues were significantly higher before and after birth?P<0.05?,however there were no significant differences after 1 week old.The concentrations of triglycerides?TG?and total cholesterol?TCHO?in the liver(P_TG=0.0022;P_TCHO<0.0001),breast(P_TG<0.0001;P_TCHO<0.0001)and thigh(P_TG<0.0001;P_TCHO<0.0001)muscle,which are lipid-metabolically active tissues,were significantly higher before and after birth,however there were no significant differences after 1 week old.Broiler chickens have high energy mobilization in the early stage of growth and development,during which the fat demand in the liver and muscles is high,and the expression of ADPN and its receptors is also high.It indicated that ADPN was closely related to lipid metabolism and energy regulation in broilers.Experiment 2 Effects of feed restriction on lipid metabolism and the gene expression of adiponectin in broilersThe energy restriction model of broilers was achieved by feed restriction.To study the effects of feed restriction on ADPN and lipid metabolism,broilers were fasted for 12 h and refeed for 2 h.The results showed that fasting decreased the concentration of TG?P=0.0184?and TCHO?P=0.0003?in plasma.Upon refeeding this phenomenon was recovered,indicating that food deprivation leads to lack of energy,which is restored with refeeding.At the same time,plasma ADPN also increased significantly after refeeding?P=0.0052?.The mRNA expression of ADPN in liver?P=0.0011?,breast?P=0.0199?,thigh?P=0.0046?and the mRNA expression of ADPNR1 in liver?P=0.0424?and duodenum?P=0.0071?were significantly increased in fasting group.This phenomenon was recovered after refeeding,too.It suggested that energy restriction may promote the utilization of fatty acids in metabolized tissues through ADPN,so as to guarantee the energy homeostasis of the body.Fasting significantly decreased duodenum?P=0.0183??because of intestinal emptying?and liver?P=0.0141?index,but fasting and refeeding did not cause significant changes in TG concentration in liver?P>0.05?,and there were no significant difference in protein levels of AMPK and CPT-1 and CPT-1 enzyme activity in liver?P>0.05?.The absence of significant difference indicated that12 h fasting did not cause significant changes in AMPK pathways.Experiment 3 Effects of insulin treatment on lipid metabolism and the gene expression of adiponectin in broilers and adipocytesA positive energy model was achieved by insulin administration.Subcutaneous abdominal injections of insulin and treatment of chicken's primary adipocytes with insulin were conducted,to study the effects of insulin on ADPN and lipid metabolism.The results showed that after insulin injection,the plasma concentration of TG?P=0.024??TCHO?P=0.0333?in broilers increased significantly,insulin concentration was significantly increased?P<0.0001?,and glucose concentration was significantly decreased?P<0.0001?,indicating that insulin injection promoted glucose utilization and lipid deposition,and the body was fully energetic.A single injection of insulin could reduce the concentration of ADPN in plasma?P=0.0487?,while there were no significant effect on the mRNA expression of ADPN and its receptors in abdominal fat,liver and breast and thigh muscle?P>0.05?.Multiple injection of insulin restored plasma ADPN levels to control levels?P>0.05?and had the tendency to decrease the mRNA expression levels of ADPN and its receptors in various tissues?0.05<P<0.1?.When adipocytes were treated with different concentrations of insulin,the mRNA expression of ADPN and its receptors were significantly decreased,they were obviously down regulated with increasing insulin concentrations(P_ADPN=0.0009;P_ADPNR1<0.0001;P_ADPNR2=0.0001).These results indicated that two metabolic hormones,insulin and ADPN,have a synergistic effect on maintaining energy homeostasis.In summary,the results showed that broiler adiponectin was closely related to lipid metabolism and energy regulation,and the change of energy state caused the response of ADPN and lipid metabolism.