Studies on oral glucose intolerance in fish

The oral glucose tolerance test, a diagnostic procedure used in the detection of human diabetes, was used to study carbohydrate metabolism in rainbow trout, Salmo gairdneri (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 hyperglycaemia resulting from glucose administration. Tolbutamidc, the sulphonylurea hypoglycaemic drug, is without effect. Possibly as an indirect result of hyperadreno-corticism, oral glucose tolerance is markedly improved in the pre-spawning female. Long-term feeding of high carbohydrate diet to goldfish Carassius auratus (L.) resulted 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 reflect a metabolism adapted to diets normally low in available carbohydrate.