Antarctic Notothenioid Fishes Do Not Display Metabolic Cold Adaptation in Hepatic Gluconeogenesis

• Main Author: Magnoni, Leonardo J.
• Format: Text
• Language: unknown
• Published: DigitalCommons@UMaine 2002
• Subjects: Fishes Antarctica; Gluconeogenesis; Oceanography; Oceanography and Atmospheric Sciences and Meteorology; Antarctic; Krebs; Antarc*; Antarctica
• Online Access: https://digitalcommons.library.umaine.edu/etd/140; https://digitalcommons.library.umaine.edu/context/etd/article/1146/viewcontent/MagnoniLJ2002.pdf

Antarctic notothenioid fishes present specializations related to their chronically cold environment, such as high lipid content in tissues (predominantly triacylglycerols, TAG). When TAGs are mobilized, they yield fatty acids and glycerol. Fatty acids are the primary fuel of oxidative muscle tissues. Gluconeogenesis from glycerol has not been studied in Antarctic fishes despite the importance of glycerol as a breakdown product of TAGs. To assess the possible importance of glycerol as a substrate for gluconeogenesis and to determine whether this pathway and Krebs cycle are metabolically cold adapted, key hepatic enzyme activities were measured in Antarctic notothenioid fishes (Notothenia coriiceps, Gobionotothen gibberifrons and Chionodraco rastrospinosus) and Subantarctic notothenioid fishes (Dissostichus eleginoides, Patagonotothen ramsayi and Eleginops maclovinus) . Citrate synthase, fructose 1,6-biphosphatase, glycerol kinase, and phosphoenolpyruvate carboxykinase enzyme activities were measured at lo, 60, 1 l o , and 2 10 C. Levels of specific metabolites in liver (glycerol, glucose and glycogen) and in serum (glycerol and glucose) were measured. My results indicate that gluconeogenesis and aerobic metabolism are not metabolically cold adapted in livers of Antarctic fishes. Levels of glycerol in plasma and liver were generally similar for all fishes studied, but surprisingly lower than the values reported for other teleost. Maximal activities for all enzymes assayed in livers of notothenioids fishes with Antarctic and Subantarctic distribution were similar when measured at the same temperature (loC). In addition, energies of activation for all the enzymes, calculated from the slope of Arrhenius plot, were similar between both groups of fishes. Lack of metabolic cold adaptation in hepatic gluconeogenesis may indicate that this pathway is of low physiological importance in both Antarctic and Subantarctic notothenioids or, more likely, that these two groups are so closely related that insufficient time has ...