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

1. The activities at 15" of three gluconeogenic enzymes, D-fructose-l,6-diphosphate, 1-phosphohydrolase (EC 3.1.3.1 l), 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 (Sulmo guirdneri) 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 pmol/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-14C]glucose. Glucose space was found to be 13.7 % of the body-weight. Gluconeogenesis in vivo amounted to approximately 45 pmol/kg body-weight per h. 4. Intraperitoneally injected [U-'*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.