Metabolic adaptation of intestine and other tissues of rat during high protein intake; [METABOLICKA ADAPTACIJA CREVA I DRUGIH TKIVA PACOVA NA POVECANI UNOS PROTEINA]

Abstract

Investigation of homeostatic mechanisms which maintain metabolic adaptation in protein excess by regulation of free amino acids, glucose and other nutritive substrate, in general, was oriented to the study of liver role. There are no adequate data on this matter for intestinal tract and other tissues. The experiments were performed on 90 days old female Wistar rats, weighing 220 g before the dietary treatment. The animals were submitted to precisely defined and controlled isoenergetic dietary treatment with different protein (casein) content in the diet: 15% (control group) and 50% (experimental group) for 18 days. After that period, the rats were anesthetized with ether in the morning and laparotomized for taking blood (portal and systemic) and tissue samples (duodenum, jejunum, ileum, liver, heart muscle, skeletal muscle, brain and uterus). Plasma levels of 20 amino acids were determined by ion-exchange chromatography technique, and in the serum the level of glucose. The content of glycogen and protein were determined in tissue samples. The results showed that high protein intake decreased the level in portal circulation. At the same lime, the glycogen content in investigated parts of the intestines was unchanged, but lower in the liver and heart muscle. By contrast, in the brain and skeletal muscle glycogen content was increased. In the 50% casein group levels of the majority of essential amino acids were increased in both circulations while the levels of nonessential amino acids showed different patterns depending on the type of circulation. While the majority of nonessential amino acids maintained their levels in systemic circulation, their levels were significantly increased in portal circulation. The highest levels in portal circulation showed alanine, proline (not-corresponding to their content in the diet casein), aspartate and arginine. In this circulation the levels of glutamate and citruline were low, level of ornitine unchanged, and that of glutamine slightly increased. The levels of the majority of nonessential amino acids in portal circulation were higher than those in systemic, particularly of alanine and proline. Glutamine was the only amino acid which did not show that difference. The nonessential/essential amino acids ratio was unchanged in systemic but significantly increased in portal circulation. With the regard to tissue protein content on high protein diet it was significantly decreased in the duodenum, jejunum, brain and skeletal muscle and increased only in the liver.