EFFECT OF DIETARY SUPPLEMENTATION WITH GLUTAMIC-ACID OR GLUTAMINE ON THE SPLANCHNIC AND MUSCLE METABOLISM OF GLUCOGENIC AMINO-ACIDS IN THE RAT

The aim of the present study was to examine the metabolic effects of a high availability of dietary glutamic acid or glutamine. A 15% casein diet was supplemented with 7.2% glutamic acid or glutamine. The present results show that both supplementations produced only a slight modification in the circulating concentrations of glutamate. Glutamic acid supplementation noticeably enhanced (+ 19%) the arterial concentrations of glutamine, but to a lesser extent than glutamine supplementation itself (+ 54%). Large amounts of alanine were released by the digestive tract in rats fed the various diets; this release was enhanced by glutamine (+ 33%) and, more markedly, by glutamic acid (+ 80%) supplementation. In the liver, glutamic acid and glutamine supplementation produced an increase in the catabolism of glycine, serine, and threonine that resulted in a drop of their peripheral concentrations, especially in muscles. The decrease in serine and threonine concentrations could be ascribed to the elevation of the serine(threonine)dehydratase activity (three fold), and the drop in glycine concentration seems to be connected to serine metabolism. It appears that the administration of glutamine (but not of glutamic acid) by the oral route could be effective in increasing its availability in peripheral tissues.