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Long‐term nutritional effects on the primary liver and kidney metabolism in rainbow trout, Oncorhynchus mykiss (Walbaum): adaptive response to a high‐protein/non‐carbohydrate diet and starvation of glucose 6‐phosphate dehydrogenase activity

Abstract:

The adaptive response of the kinetics of glucose 6‐phosphate dehydrogenase (G6PDH) was studied in trout liver and kidney after feeding (control or high‐protein/non‐carbohydrate diet) or starving for 30 days, as well as influences on growth and other nutritive parameters. Typical Michaelis‐Menten kinetics were found for the hepatic catalysis of G6PDH under all conditions studied, without evidence of sigmoidicity. The administration of a high‐protein/non‐carbohydrate diet (61.0% protein, 7.9% lipids) produced no significant changes in specific activity or other kinetic parameters of the liver enzyme. This nutritional situation caused a significant daily increase in relative growth (20%) and feed efficiency (13.5%), as well as a 13% decrease in the protein‐conversion efficiency, with respect to the control diet (46% protein, 8% lipids, 22% carbohydrates). On the other hand, long‐term starvation (30 days), as a lipolytic condition, significantly decreased the activity and catalytic efficiency of hepatic G6PDH, by almost 45%, without significant changes in the Km and activity‐ratio values. These changes agree with a fall in the intracellular concentration of the enzyme as a consequence of a protein‐repression process. The activity of the renal G6PDH was less than in the liver of control fish, and no variation in kinetics was found under the high‐protein diet or starvation. This behaviour clearly demonstrates that the kidney pentose‐phosphate pathway showed no adaptive response in relation to synthesis of fatty acids and other lipids. Copyright © 1995, Wiley Blackwell. All rights reserved