Studies on oral glucose intolerance in fish

Abstract

The oral glucose tolerance test, a diagnostic procedure used in the detection of human diabetes, was used to study carbohydrate metabolism in rainbow trout, Sulmo guirdneri (Richardson). Fish exhibited pronounced and persistent hyperglycaemia on oral glucose administration. Hyperglycaemia was accompanied by decrease in blood amino acids, serum free fatty acids and cholesterol and marked increase in hepatic storage of glycogen. The incidence of oral glucose intolerance results, at least in part from insufficient circulating insulin. Exogenous insulin exerts a hypoglycaemic action and effectively abolishes the hyperglycacmia resulting from glucose administration. Tolbutamidc, the sulphonylurea hypoglycaemic drug, is without effect. Possibly as an indirect result of hyperadrenocorticism, oral glucose tolerance is markedly improved in the pre-spawning female. Longterm feeding of high carbohydrate diet to goldfish Cnrussiirs aurutus (L.) resultcd in gross hepatomegaly due to excessive hepatic glycogen accumulation and, possibly, fatty change of the liver. Protein metabolism was impaired as evidenced by protein depletion. Such degenerative changes in liver metabolism are probably a direct result of oral glucose intolerance and reflcct a metabolism adapted to diets normally low in available carbohydrate.

Molecular Characterization and Identification of Facilitative Glucose Transporter 2 (GLUT2) and Expression of Related Glycometabolism in Response to Different Starch Levels in Blunt Snout Bream (Megalobrama amblycephala)

“…So high GK expression associated with dietary carbohydrate intake, one consequence of which is the relatively high levels of glycemia [40,41,52], which supported our experimental results. PK is the final step of glycolysis.…”

Hormonal regulation of glucose clearance in lactating northern elephant seals (Mirounga angustirostris)

“…We would expect that the lower carbohydrate diet of carnivores would have important impacts on glucose metabolism; however, some studies do suggest that the high protein diet of carnivores may be associated with impaired ability for glucose clearance. Penguins (Chieri et al, 1972), barn owls (Myers and Klasing, 1999), rainbow trout (Palmer and Ryman, 1972), white sturgeon (Hung, 1991) and American alligators (Coulson and Hernandez, 1983) exhibited reduced glucose clearance when compared to omnivores. We are aware of no similar studies in wild mammalian carnivores.…”

Effects of insulin infusion on glucose homeostasis and glucose metabolism in rainbow trout fed a high-carbohydrate diet

“…Although a deficiency in insulin secretion was initially thought to be the basis for poor glucose utilization following a glucose load (Furuichi and Yone, 1981;Palmer and Ryman, 1972), plasma insulin levels in piscine species were later found to be even higher than those in mammals (Mommsen and Plisetskaya, 1991). Insulin functions primarily as an anabolic hormone by stimulating postprandial glucose uptake by liver and skeletal muscle, depressing rates of hepatic gluconeogenesis, and activating glycogenesis and lipogenesis.…”

“…Carnivorous fish species, including rainbow trout (Oncorhynchus mykiss), are traditionally considered as glucose intolerant (Moon, 2001;Wilson, 1994), primarily owing to the prolonged hyperglycemia experienced after a glucose load or the intake of a carbohydrateenriched meal (Bergot, 1979;Palmer and Ryman, 1972). At the metabolic level, some of the enzymes involved in glucose metabolism, such as glucokinase (liver), phosphofructokinase (liver and muscle) and pyruvate kinase (liver and muscle), are inducible by dietary carbohydrates, as described in mammalian systems (Fideu et al, 1983;Panserat et al, 2000a;Panserat et al, 2001c), yet an atypical regulation of other actors involved in glucose metabolism is reported.…”