HYPOMETABOLISM WITH FASTING IN THE YELLOW PERCH (PERCA-FLAVESCENS) - A STUDY OF ENZYMES, HEPATOCYTE METABOLISM, AND TISSUE SIZE

This study analyzes the total potential of the liver in terms of enzyme activities and hepatocyte flux in fed and fasted yellow perch. A 7-wk fast decreased the hepatosomatic index from 1.99 to 0.85 with an equivalent increase in liver DNA concentration, indicating atrophy of the liver with fasting. Total contents of liver and muscle glycogen and protein declined. As a function of body weight, enzyme activities all decreased with the exception of the lipid-catabolizing enzymes; gluconeogenic enzymes declined less than those of glycolysis, the NADPH-producing enzymes, and citrate synthase. No enzyme activities increased with fasting as a function of body weight. Phosphorylation-related changes in regulatory enzymes support the protection or maintenance of gluconegenesis. Lactate, alanine, and glycerol flux to glucose in isolated hepatocytes all decreased as a function of tissue DNA, as did alanine flux to CO2. Again, no increases in flux were noted with fasting. These data demonstrate that after a 7-wk fast yellow perch are hypometabolic. The importance of considering changes in tissue size in the analysis of environmental stressors is discussed.