An investigation of the effects of nutritional status on the action of insulin in rainbow trout (Salmo gairdneri) Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/pc289n49p

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  • Three studies were conducted to evaluate the relationship between insulin and nutritional parameters in rainbow trout. In the first study effects on growth parameters and tissue composition of rainbow trout were investigated following injection of bovine insulin at two dose levels every 48 hr for 56 days. In addition, [¹⁴C]-leucine incorporation into plasma, liver, and skeletal muscle was studied for the two insulin treatments and a group of the saline-injected controls given a single shock-dose of insulin (5.0 IU/kg). Hypoglycemic responses were observed with all insulin treatments. In comparison to controls, high insulin treatment gave a significant body weight increase. At both levels, insulin increased the content of protein, lipid, and also the incorporation of [¹⁴C]-leucine activity in skeletal muscle. Simultaneous decreases in specific activity of plasma and liver tissue indicated a net movement of [¹⁴C]-leucine toward the peripheral musculature. No effect of the hormone was seen on the glycogen content of liver or muscle tissue over the 56-day period. In a second study, the effect of bovine insulin on tissue incorporation of [¹⁴C]-glucose and [³H]-leucine was investigated in fed and fasted rainbow trout reared on a control and high-protein diet. Insulin produced marked hypoglycemia and mobilization of liver glycogen in all treatments. Although insulin gave no evidence of glycogenic stimulation it did appear to promote oxidative clearance of [¹⁴C]-glucose. Compared to [¹⁴C]-glucose much greater tissue incorporation of [³H]-leucine was observed in fasted fish; insulin stimulated the incorporation of [³H]-leucine into skeletal muscle protein. In plasma, liver, and skeletal muscle of all treatments, the summed specific activities of [³H]-leucine was considerably greater than that of the summed values of [¹⁴C]-glucose following insulin administration. Four weeks of fasting apparently lowered basal metabolism but no changes were observed in plasma glucose and glycogen stores. There was some evidence of gluconeogenic activity in the high protein-fasted fish and the data indicated in all fasted treatments a stimulation of [¹⁴C]-glucose and [³H]-leucine metabolism following insulin administration. As a third investigation, [¹²⁵I]-iodoinsulin binding studies in the presence of a concentration range of bovine insulin were conducted to establish specific insulin binding levels in erythrocytes, skeletal muscle plasma membranes and isolated hepatocytes of rainbow trout reared on control-, high-protein and high-carbohydrate diets. Negative cooperativity was observed and receptor concentrations and apparent dissociation constants established for each preparation. No differences of specific binding attributed to diet were detected in either erythrocytes or skeletal muscle plasma membrane preparations, However, the receptor concentration of isolated hepatocytes from high-carbohydrate reared trout was increased. This contrasted to comparable mammalian studies. In view of an apparent depression of receptor concentration in skeletal muscle plasma membranes and isolated hepatocytes of high-protein reared trout, these data were interpreted according to the reciprocal relationship observed between endogenous insulin and insulin receptor concentrations established for mammals. Unlike mammals where glucose was shown to be the primary insulin secretagogue, endogenous insulin levels in rainbow trout have been closely correlated to circulatory amino acids and are thought to be primarily controlled by these protein metabolites.
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