Study For The Metabolic Fate Of Glycine And Alanine In The Porcine Liver

The objective of this study was to determine the metabolic fate of glycine(Gly) and alanine(Ala) and the relationship between Gly and Ala and urea synthesis in the porcine liver. In experiment 1, Duroc × Landrace × Yorkshire(DLY) barrows weighing 20 ± 1.0 kg, 40 ± 1.0 kg, 60 ± 1.0 kg(n = 6 per weight class) were conducted to study the quantitative changes of Gly and Ala in the liver. The barrows were surgically fitted with permanent catheters in the mesenteric vein, portal vein, carotid artery, and hepatic vein. All barrows had ad libitum access to fresh water and were fed equal amounts at 0800, 1600 and 2400 daily. After barrows were recovered from the surgeries, a priming dose(15 m L) of p-aminohippuric acid(PAH) solution was given via the mesenteric vein at 0730 h, followed by a constant infusion of PAH solution at a rate of 0.8 m L/min. Sixty min after administration of the priming dose, 5-m L blood samples were collected from each barrow from the hepatic vein, portal vein and carotid artery at 0830, 1000, 1200, 1430, and 1730. The results showed that the metabolic rate of Gly and Ala in the liver of barrows weighing 20, 40, 60 kg were 15.2 mg/min, 29.7 mg/min and 38.6 mg/min, respectively, accounting for 57.2%, 57.4% and 60.3% of amino acids metabolized in the porcine liver.In experiment 2, tweleve healthy Duroc × Landrace × Yorkshire(DLY) barrows(40 ± 1.0 kg) were used to study the metabolic fate of Gly and Ala in the liver.. The barrows were surgically fitted with permanent catheters in the mesenteric vein, portal vein, carotid artery, and hepatic vein. All barrows had ad libitum access to fresh water and were fed equal amounts at 0800, 1600 and 2400 daily. After recovery from surgery, a priming dose(15 m L) of L-[15N]alanine solution or L-[15N]glycine solution was infused into six barrows via portal vein catheter at 0730 h, followed by a constant infusion of L-[15N]alanine or L-[15N]glycine solution at a rate of 0.8 m L/min. A priming dose(15 m L) of PAH solution(15 mg/m L) was given via the mesenteric vein at 0730 h, followed by a constant infusion of PAH solution at a rate of 0.8 m L/min. Sixty min after administration of the priming dose, 5-m L blood samples were collected from the portal vein, carotid artery, and hepatic vein catheters of each barrow, at 0830 h, 1000 h, 1200 h, 1430 h, and 1730 h. The results showed that the ratios of urea derived from Gly and Ala to total urea produced in liver were 18.5% and 16.7%, respectively.Experiment 3 was conducted to study the effects of Gly and Ala on urea synthesis in the hepatocytes of piglets.The primary hepatocytes, isolated from a piglet at 1 week of age, were treated with Gly at dose of 10 mg/m L, 20 mg/m L, 40 mg/m L and 80 mg/m L or Ala at dose of 10 mg/m L, 20 mg/m L and 40 mg/m L. The results showed that supplementing Gly with a dose of 40 mg/m L increased the concentration of urea in the hepatocyte(P<0.05). Supplementing 10 mg/L Ala increased the concentration of NH3-N in the hepatocyte(P<0.05).This study indicate that the Gly and Ala are important precursors of urea synthesis.