Organ and plasma amino acid concentrations are profoundly different in piglets fed identical diets via gastric, central venous or portal venous routes.

In a previous study in piglets fed identical diets intravenously, intraportally or intragastrically, we determined that small intestinal atrophy affects nitrogen metabolism to a greater extent than liver by-pass. Because whole-body amino acid homeostasis is dependent on interorgan metabolism, we also measured the free amino acid concentrations in liver, small intestinal mucosa and kidney in order to study alterations in amino acid metabolism within these organs. Piglets (n = 15; 2-4 d old) were fed identical diets continuously for 8 d via gastric (IG), portal (IP) or central venous (IV) catheters. Concentrations of all measured amino acids were affected by route of feeding in one or more organs. In particular, urea cycle amino acid concentrations were altered in plasma and mucosa of IV and IP pigs, suggesting that arginine synthesis by an atrophied gut may have been limited. Furthermore, most indispensable amino acid concentrations were lower in IP pigs for all organs vs. IG pigs; however, except for phenylalanine, plasma concentrations of these amino acids were not different, demonstrating the liver's "smoothing" capability. Gut atrophy in both IV and IP pigs resulted in significantly lower concentrations of all indispensable amino acids compared with IG pigs. Alterations of all amino acids in various organs due to route of feeding suggest that more detailed analyses of regulatory mechanisms and amino acid interactions on interorgan amino acid metabolism are necessary for all amino acids.