| Yak is mainly distributed in the Qinghai-Tibetan Plateau, where the cold season last seven months every year, and the yaks chronically suffer from hungry. This is the primary cause responsible for yak off-fat and death. Therefore, disaster resistance and livestock protection became a normal work in cold season there.The Maiwa yak were used in this study to explore the mechanisms of yak intramuscular fat and liver fat catabolism and possible regulatory pathways under starvation condition, to provide experimental data for yak nutrition research and disaster resistance and livestock protection in cold season.Eight 3 years old yaks, which were healthy, in good growth condition and consistent in body weight (110.3±5.85 kg) were selected and were randomized allocated into two groups (the control vs fasting group). The yaks of control group were slaughtered at day 1 and samples were collected.The other group was used as experimental treatment, suffering from starvation, and blood samples were collected through jugular vein on day 1,3,5,7,9 respectively. After the last blood sampling, the yaks were also slaughtered for tissue samples collection. The results showed as folowing:(1) The yaks live weight and carcass weight decreased significantly after starvation (P<005).(2) The fat mobilization of yaks in muscle tissues and liver had different spatial characteristics. The fat content of biceps femoris and semitendinosus muscle decreased by 60.2% and 48.7%(P<0.01), while the fat content of psoas muscle, longissimus muscle, sinew and liver did not change significantly after starvation (P>0.05). The long-chain saturated fatty acids in liver and polyunsaturated fatty acids in liver and longissimus muscle were significantly lowered (P<0.05), while the C17:0, C18:0 saturated fatty acids in liver and total saturated fatty acids in longissimus muscle were significantly increased(P<0.05).(3) The yak blood glucose concentration was significantly lowered after short-term starvation (P<0.05), though with the extension of starvation, the changes were not significant (P>0.05).(4) The triglycerides and non-esterified fatty acid in yak serum were significantly increased after starvation (P<0.05), while lipid metabolism intermediates (β-hydroxybutyric acid, acetylsalicylic acid and oxaloacetate) were significantly lowered after starvation (P<0.05).The β-hydroxybutyric acid and acetylsalicylic acid concentrations in longissimus muscle and liver were significantly increased after starvation(P<0.01), while the oxaloacetic acid concentrations in longissimus muscle and liver were significantly lowered (P<0.05).(5) The serum glucagon and norepinephrine were significantly increased with the extension of starvation, whereas the insulin was significantly reduced (P<0.05). In the first five days after starvation,the glucagon peaked and then decreased significantly(P<0.05),finally remained in the levels significantly higher than that before the begining of starvation(P<0.05). The insulin was significantly reduced after short term starvation (P<0.05). After the first three days of starvation the insulin was gradually restored, but remained in the levels significantly lower than that before the begining of starvation (P<0.05).The glucagon in longissimus muscle, semitendinosus muscle and liver were significantly elevated(P<005). The norepinephrine in longissimus muscle was increased (P<0.05), while it was decreased in liver and semitendinosus muscle (P<0.05). The insulin was significantly reduced in the liver(P<0.05), but was significantly increased (P<0.05) in the semitendinosus muscle.(6) The serum enzymes that break down fat (hormone-sensitive enzyme and adipose tissue triglyceride hydrolases) were significantly increased (P<0.05), and reached at the highest level in the first three days of starvation. The hormone-sensitive lipase, adipose tissue triglyceride hydrolases concentration and lipoprotein lipase activity in longissimus muscle, semitendinosus muscle and iver were also significantly increased (P<0.05).(7) The mRNA expression of phosphatidyiinosiiol 3-kinase and protein kinase B in longissimus muscle were significantly lowered (P<0.05), and the hormone-sensitive lipase was significantly increased (P<0.05). The mRNA expression of adipose trigiyceride lipase was increased by 270%. The mRNA levels of phosphatidylinositol 3-kinase and protein kinase B in semitendinosus muscle were significantly increased (P<0.01). The adipose triglyceride lipase and hormone-sensitive lipase mRNA levels were increased by140% and 120% in semitendinosus muscle (P<0.05). The mRNA expression of acyl-CoA dehydrogenase long-chain,3-hydroxy-3-methylglutaryl-CoA synthase were extremely significant increased (P<0.01), while the carnitine palmitoyl transferase 1 mRNA expression was significantly elevated in the liver (P<0.05).In summary, the live weight and carcass weight are reduced and the content of intramuscular fat and fat acid oxidation are accelerated by starvation. The hormones secretion and key enzymes that regulates lipolysis, fatty acid β-oxidation and P13K/AKT pathway are affected.The activity of key enzymes regulate fat breakdown in blood, longissimus muscle, semitendinosus muscle and liver are increased after starvation. The fat content of biceps femoris and semitendinosus muscle are reduced, as well as the long-chain saturated fatty acids in the liver and polyunsaturated fatty acids in the liver and longissimus muscle. The fat metabolism intermediates (β-hydroxybutyric acid, acetylsalicylic acid) in dorsi muscle and liver are increased. It indicates that the yak reduces fat deposition in muscles, promote the hydrolysis of triglycerides in musclesand fatty acid β-oxidation in the liver, reduce the ability of extrahepatic tissues to use the ketone, to maintain glucose concentrationat a low level to support energy supply and maintain their life. |
PDF Full Text Request