Long-term effect of a high-protein/non-carbohydrate diet on the primary liver and kidney metabolism in rainbow trout ( Salmo gairdneri)

Abstract

Several aspects of the metabolic adaptation of trout liver and kidney to a high-protein diet were studied. Under this nutritional situation there were significant increases in the activities of the glycolytic enzymes phosphofructokinase (PFK) and pyruvate kinase (PK) from both tissues but with a different molecular basis. PFK activity was increased at subsaturating substrate concentrations, with a decrease in Michaelis constant ( K m) values of about 70% in both tissues and without changes in the maximum velocity ( V max). The activity of PK was increased all along the saturation curve, approximately 70% and 20% in liver and kidney respectively. However, no changes in the activities of glucose 6-phospate dehydrogenase (G6PDH) were detected. On the other hand, the activity of the gluconeogenic enzyme fructose 1,6-bisphosphatase (FBPase) from both tissues was increased only at cellular substrate concentrations. With respect to amino acid metabolism, liver alanine aminotransferase (AAT) was enhanced at all substrate concentrations, with a significant increase of almost 50% in the V max, without changes in the renal activity. Glutamate dehydrogenase (GDH) activity was almost 300% and 100% of control values, in liver and kidney respectively, observations which are in good agreement with the role of this enzyme in the two tissues.