| Three experiments were conducted to determine whether AMP-activated protein kinase (AMPK) might involve in energy metabolic response to stress in piglets. On the basis of validating AMPK activity assay procedure, we studied tissue distribution of the AMPK, effects of stress on the AMPK activity, and whether AMPK might mediating lipid metabolism pigs under stress .Exp. 1 Tissue Distribution of AMPK and the Effects of Heat Stress on AMPK Activity in PigletsAMPK was found in vast tissues in rats, and it was activated by metabolic stresses that deplete cellular ATP. In this study, a single-factor design was employed to explore the tissue distribution of AMPK and the effect of heat stress on AMPK activity in piglets. After a 10-d adjustment, 10 crossed (Duroc x (LandraceX Taihu) ) pigs about 60 days of age were randomly allotted to 2 treatments (control and heat stress) with five replicates per treatment and one pig per replicate. The room temperature of control and heat stress was 25 ± 1℃ and 36± 1 ℃, and relative humidity was 50-60% and 40-50% respectively . The trial was conducted for 72 hours. Body gain and feed intake, serum alkaline phosphatase(ALP), lactic acid dehydrogenase(LDH), glucose, triglyceride and total cholesterol levels, the kinase activity in liver, skeletal muscle, heart and duodenum were examined respectively at the end of the trial. The results showed that AMPK was present in liver, skeletal muscle, heart and duodenum of pigs with highest activity in skeletal muscle and lowest activity in liver. Heat challenge reduced growth performance of pigs. Average feed daily intake and average daily gain were reduced by 19.21% and 39.87% (p<0.05) respectively, and F/G was enhanced 41.54%. At the same time, ALP activity was reduced by 50.55% and LDH was increased by 21.35%. After 72-hour heatchallenge, the AMPK activities in liver, skeletal muscle and duodenum were increased by 10.53%, 35.00% and 28.04% respectively, and correspondingly with the decrease of ACC activity by 7.57%, 11.82% and 35.23% respectively . AMPK and ACC activities in heart were not altered under stress. Serum glucose, triglyceride and total cholesterol levels tended to be reduced. These results indicated that heat stress influenced the tissue AMPK activities. It was proposed that AMPK might be involved in energy metabolic response to stress of pigs.Exp. 2 . Effects of Activator and Inhibitor of AMPK on Lipid Metabolism in Hepatocytes of PigletsAMPK is activated in response to 5-amino-imidazolecarboxamide riboside(AICAR), a cell-permeable compound that is metabolized to its monophosphorylated derivative, ZMP, which mimics the multiple stimulatory effects of AMP on AMPK. Activated AMPK stimulates fatty acid oxidation in rat liver and skeletal muscle. To determine whether AMPK might regulate lipid metabolism, we studied lipid metabolism in piglet cultured hepatocytes in the presence of 0.2mmol/l AICAR, or0.2mmol/l 8Br-AMP.. The results showed that adding 0.2mmol/l AICAR to cultured hepatocytes activated AMPK and inhibited ACC significantly. AMPK activity at 60min after incubation was increased by 47.00% (p<0.05), and ACC activity was decreased by 68.8% (p<0.05) .In contrary, adding 0.2mmol/l 8Br-AMP to cultured hepatocytes inhibited AMPK and activated ACC with the decrease of AMPK activity by 22.37% and the increase of ACC activity by 9.0% at 60-min incubation. Adding AICAR increased fatty acid oxidation and the production of acid-soluble metabolites(ASM) isotoped with 14C was increased by 25.58%, 39.15% (p<0.05 ) and 24.23% (p<0.01) after incubating for 30min, 60min and ISOmin respectively. At the same time, adding AICAR decreased [14C]oleate incorporation into triglycerides, phospholipids plus monoglycerides, cholesterol,and cholesteryl ester. Adding Br-AMP decreased fatty acid oxidation with lower production of 14CO2 and [14C]ASM than control at the time of 3h post-incubation. At the same time, adding 8Br-AMP increased [14C]oleate incorporation into triglycerides, phospholipids plus monoglycerides, cho...
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