The hepatic extraction of plasma free amino acids and response to hepatic portal venous infusion of methionine sources in anesthetized SCWL males (Gallus domesticus)

This study was conducted to investigate the hepatic extraction of plasma free amino acids in anesthetized Single Comb White Leghorn (SCWL) males (Gallus domesticus). SCWL males were anesthetized and implanted with cannulae in the carotid artery, hepatic vein, hepatic portal vein and the left hepatic duct. Free amino acids in plasma and bile were determined before, during and after 30-min infusions of Saline (control), DL-Methionine (DL-Met) or DL-2-hydroxy-4-methylthio-butanoic acid (DL-HMB) into the hepatic portal vein. Hepatic extraction rates (HER) of amino acids were calculated based on the concentration of amino acids in plasma multiplied by estimations of blood flow in the hepatic portal vein, hepatic artery and hepatic vein. For the non-essential amino acids, alanine had the highest HER (46%). The liver also removed more than 20% of hepatic inflow of tyrosine and asparagine with substantial extraction (14-18%) of serine, glycine and glutamine, also. In contrast, less than 5% of hepatic inflow of glutamate and cystine were removed by liver. For the essential amino acids, HER for methionine, histidine and phenylalanine were 30, 14 and 17%, respectively, with less than 5% for branched-chain amino acids, lysine, arginine and threonine. Biliary secretion of amino acids represented a small percentage (<0.2%) of total hepatic extraction turnover of the amino acids. Infusion of methionine sources, DL-MCt and DL-HMB, had no effect on hepatic metabolism of amino acids other than methionine. The results demonstrated for the first time, the hepatic extraction of circulating free amino acids in avian species in vivo. (C) 2001 Elsevier Science Inc. All rights reserved.