The hepatic amino acid system A transport activity, is up-regulated in obese Zucker rats

The utilization of L-alanine by liver is dependent on amino acid uptake fro m blood. This uptake, mainly mediated by the A transport system, may be reg ulated by different nutritional and physiologic conditions. The regulation of this transport system by diets with different protein content teas teste d irt lean and obese Zucker rats. High-protein (HP) and low-protein (LP) di ets led to changes in the rats' growth patterns, especially in lean animals . However, homeostasis was relatively well maintained, as seen in plasma va lues, in spite of the increased urea production in the HP groups and increa sed triacylglycerides in the LP groups. The obese animals rook lip L-alanin e at a higher rate than the lean animals. Obesity led to the emergence of a high-affinity component (K-M approximately 0.1-0.2 mM) in the transport sy stem, which was not dependent on the protein content of the diet. This comp onent has a IO-Sold increase in affinity for L-alanine, but with an approxi mately 3- to 5-fold reduction in maximal velocity of transport. (C) Elsevie r Science inc. 1999. All rights reserved.