HEPATIC-UPTAKE OF AMINO-ACIDS IMMEDIATELY AFTER LIVER-TRANSPLANTATIONIS WELL PRESERVED DESPITE ALTERED PLASMA PROFILES

Background: The liver is one of the principal organs responsible for t he uptake and release of amino acids in the body. The ability of the t ransplanted liver to clear plasma amino acids is associated with a fun ctioning allograft. However, clinical assessment is limited by the ina bility to access the portal vein postoperatively. Therefore, using a p orcine liver transplant model, we examined (1) the plasma levels of am ino acids presented to the new hepatic allograft and (2) the capacity of the new allograft to clear these amino acids from the circulation. Materials and Methods: Two groups of commercially bred pigs were studi ed: a control group (n = 8) underwent laparotomy and a transplanted gr oup (n = 6) underwent orthotopic liver transplantation (LT) using veno -venous bypass. All pigs had catheters placed in the carotid artery an d portal and hepatic veins and ultrasonic transit time flow probes pla ced around the hepatic artery and portal vein. Plasma profiles of 23 a mino acids were analyzed by high-pressure liquid chromatography. Hepat ic balances of amino acids, using arteriovenous difference techniques coupled with hepatic blood flows, were also analyzed on postoperative day 1. Results: Neither portal vein blood flow (703 +/- 74 ml/min vs 6 66 +/- 82 ml/min) nor hepatic artery blood flow (322 +/- 43 ml/min vs 209 +/- 59 ml/min) was significantly different between the control and the transplanted groups, respectively. The transplanted group had sig nificantly increased plasma levels of alanine (135 +/- 13 mu mol/l vs 382 +/- 72 mu mol/l), hydroxyproline (30 +/- 5 mu mol/l vs 60 +/- 9 mu mol/l), methionine (25 +/- 2 mu mol/l vs 55 +/- 10 mu mol/l), ornithi ne (36 +/- 5 mu mol/l vs 141 +/- 33 mu mol/l), phenylalanine (84 +/- 5 mu mol/l vs 120 +/- 12 mu mol/l), threonine (75 +/- 9 mu mol/l vs 159 +/- 27 mu mol/l), and tryptophan (17 +/- 2 mu mol/l vs 31 +/- 4 mu mo l/l). The transplanted group also had significantly decreased plasma l evels of isoleucine (122 +/- 12 mu mol/l vs 85 +/- 8 mu mol/l) and tau rine (71 +/- 7 mu mol/l vs 35 +/- 7 mu mol/l). These individual amino acid changes were not accompanied by impairment in the net hepatic ami no acid balance or the hepatic fractional extraction of amino acids be tween the two groups. Conclusion: These results suggest that the circu mstances associated with liver transplantation alter the fasting amino acid profile immediately postoperatively. However, liver transplantat ion does not impair the normal hepatic allograft uptake of most plasma amino acids. Thus, the changes observed in the circulating levels of amino acids may represent alterations in nonhepatic production and/or utilization. Furthermore, altered plasma amino acid profiles following liver transplantation are not necessarily indicative of impaired hepa tic allograft amino acid metabolism. (C) 1998 Academic Press.