ABSTRACT
Glutamine is, at a concentration of ~600 µmol/L, the most abundant amino acid in mammalian plasma. The number of goblet cells in the colon is much higher than in the small intestine. The selective expression of glutamine synthetase (GS) in goblet cells raised the question whether the high enzyme activity in the colon relative to the small intestine was due to the much higher number of goblet cells in the colon or to a difference in enzyme activity per goblet cell. The finding that GS protein was only found in goblet cells and that the density of goblet cells determined the distribution of GS in the intestines was unexpected in view of earlier immune and in situ hybridization stainings. Feeding caused the concentration of amino acids in the portal vein to increase ~8% relative to the corresponding amino acids in 24 h-fasted control mice, whereas the concentration of glutamine declined to ~55% and that of alanine increased ~30%.
