| The objective of this study was to determine the effects of dietary protein levels on amino acid metabolic transformation in the liver of piglets. The research included four experiments:Trial 1 was conducted to study the effects of dietary protein levels on plasma amino acid concentrations in portal vein and hepatic vein and net flux in portal vein of piglets. Eighteen healthy Duroc × Landrace × Yorkshire (DLY) piglets (20±1.0 kg) were implanted into portal vein, arterial vein, mesenteric vein and hepatic vein by blood intubation techniques and randomly allocated to 3 treatments with 6 piglets per group. Piglets in 3 treatments were fed a maize-soybean meal diet containing 20% CP,17% CP, 14% CP, respectively. During the experiment, food and water were provided ad libitum. Piglets were fed at 0800,1600 and 2400, respectively. After piglets were recovered from the surgeries, blood samples were collected from hepatic vein, portal vein and carotid arterial at 0730,0930,1130 and 1430. The results showed that in addition to Glutamic (Glu), the other amino acid concentrations in portal vein were higher than hepatic vein (P<0.05); with the decrease of protein levels, the plasma of Total Amino Acid (TAA) and Non-Essential Amino Acid (NEAA) concentrations in the portal vein and hepatic vein and the Essential Amino Acid (EAA) concentrations in the hepatic vein were reduced (P<0.05), but the plasma of EAA concentrations in the portal vein were not influenced by dietary protein levels (,P>0.05). The ratio of EAA and NEAA concentrations in portal vein were 1.21,1.23 and 1.24 at CP 20%, CP 17% and CP 14%, respectively, they were higher than hepatic vein (P<0.05). Decreased diet protein levels did significantly reduced net Portal-Drained Viscera (PDV) of TAA and NEAA (P<0.05), but did not significantly affect net PDV of EAA (P>0.05); the ratio of EAA and NEAA net flux in PDV were 1.70,2.08 and 2.06 at CP 20%, CP 17% and CP 14%, respectively. There was no significant difference on absolutely variation of plasma TAA in the liver of piglets (P>0.05), with the decrease of protein levels, variation of the NEAA would be reduced (P<0.05), but the EAA was on the contrary (P<0.05); with the decrease of protein levels, the ratio of absolutely variation of EAA and NEAA were increased (P>0.05); Glu would increase after metabolized by the liver.Trial 2 was conducted to study the effects of dietary protein levels on metabolism in piglets, the experimental design was the same as that of trial 1. The results showed that, with the increase of protein levels, Glucose (GLU) and Blood Urea Nitrogen (BUN) concentrations in portal vein and hepatic vein were significant increased (P<0.05), but GLU and BUN concentrations were not significantly affected in carotid vein (P>0.05). Total Protein concentrations in the portal vein, hepatic vein and arterial vein were not influenced by dietary protein levels (P>0.05).Trial 3 was conducted to study the effects of dietary protein levels on amino acid metabolism enzyme in piglet’s liver. Fifty-four healthy 28 d DLY piglets were randomly allocated into three treatments with 18 piglets per group. Piglets in 3 treatments fed a maize-soybean meal diet containing 20% CP,17% CP,14% CP, respectively. The experiment lasted 7 d adaptation period and 45 d test period. Six piglets were selected from each group to be slaughtered on d 10, d 25 and d 45 respectively, and the samples of livers were collected. The results showed that, with the increased of protein levels, the glutamic-pyruvic transaminase, glutamic-oxalacetic transaminase and glutamine synthetase activity were significantly increased in the liver of piglets (P<0.05), but the glutamic acid dehydrogenase activity did not significant difference (P>0.05).Trial 4 was conducted to study the effects of dietary protein levels on the mRNA expressions of amino acid transporter in the liver of piglets. The experimental design was the same as trial 3. The results showed that, with the increase of protein levels, the mRNA expressions of amino acid transporter SLC6A15, SLC6A20, SLC36A1 and SLC38A2 would be rose.Summary:In addition to reducing the protein levels and supplementing EAA in diet, it needed to add a specific proportion of NEAA. It not only reduced emissions of nitrogen and maintained to the activity of amino acid metabolism enzyme and the expressions of amino acid transporter, but also improved the conversion efficiency of amino acid metabolism in the liver of piglets. |
