Long-term nutritional effects on the primary liver and kidney metabolism in rainbow trout (Oncorhynchus mykiss). II. Adaptive response of glucose 6-phosphate dehydrogenase activity to high-carbohydrate/low-protein and high-fat/non-carbohydrate diets

Abstract

The influence of long‐term administration of high‐carbohydrate/low‐protein and high‐fat/non‐carbohydrate diets were studied in relation to kinetic behaviour of glucose 6‐phosphate dehydrogenase in liver and kidney of rainbow trout. In all cases studied, the saturation curves of these enzyme showed typical hyperbolic kinetics without evidence of sigmoidicity. After 30 days of feeding with a high‐fat diet (170 g kg−1), there was a significant decrease in Vmax and specific activity (45%) as well as catalytic efficiency (39%) without changes in Km or activity ratio of hepatic glucose 6‐phosphate dehydrogenase. These changes agree more with a clearly decreased cell concentration than with an inhibition of the pre‐existing enzyme. The administration of a high‐carbohydrate diet (60 g kg−1), contrary to what was previously thought, decreased Vmax by 21% and specific activity and catalytic efficiency by 30%, without significant changes in the other kinetic parameters of the hepatic enzyme. The kinetic behaviour under these nutritional conditons was due to the rejection of this diet by the fish and thus could be considered a low‐feeding situation. On the other hand, no variations in the kinetics of renal glucose 6‐phosphate dehydrogenase were found, clearly demonstrating that in this organ, the pentosephosphate pathway showed no adaptive response related to fattyacid and other lipid synthesis. The activity of the renal enzyme was consistently half that of the hepatic enzyme.

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“…A atividade destas enzimas é normalmente afetada pela temperatura da água e por fatores hormonais, mas principalmente pela composição da dieta e pela freqüência de alimentação e podem ser utilizada como indicador do perfil nutricional de algumas espécies (Méton et al, 2003;Sanden et al, 2003;Fritz & Kletzien, 1987, citados por Sanden et al, 2003.…”

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The Effect of Feeding Varying Levels of Soybean Meal in High‐Nutrient‐Density Diets on Growth Performance and Body Composition of Juvenile Atlantic Salmon

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