The effect of dietary composition and of insulin on gluconeogenesis in rainbow trout ( Salmo gairdneri )

Abstract

1. The activities at 15° of three gluconeogenic enzymes, d -fructose-1,6-diphosphate, 1-phosphohydrolase ( EC 3.1.3.11), pyruvate carboxylase ( EC 6.4.1.1) and phosphoenolpyruvate carboxykinase (4.1.1.32), were determined in liver, kidney, gill and muscle of rainbow trout ( Salmo gairdneri ) given a commercial diet. The results indicated that liver and kidney are the main sites of gluconeogenesis. 2. Glucose formation from pyruvate was approximately 6 μmol/h per g wet weight at 15° in liver slices of trout given a commercial diet. 3. Glucose diffusion space in trout was measured by the dilution principle after intravascular injection of a trace dose of [U- 14 C]glucose. Glucose space was found to be 13.7% of the body-weight. Gluconeogenesis in vivo amounted to approximately 45 μmol/kg body-weight per h. 4. Intraperitoneally injected [U- 14 C]alanine was quickly converted to glucose. Maximal incorporation of alanine into glucose occurred 6 h after alanine administration. 5. Rainbow trout given a high-protein diet gained in weight significantly during a 4-week period. Those given a high-carbohydrate diet did not make a significant weight gain over the same period. Gluconeogenesis from alanine was markedly reduced in fish given the high-carbohydrate diet. There was no significant difference in gluconeogenesis from alanine in fish given a high-protein diet and fish which were fasted for 21 d.6. Gluconeogenesis from alanine in trout was suppressed by intravenous injection of insulin. This effect was found both in trout given a high-protein diet and in fasted trout.