Hypometabolism with Fasting in the Yellow Perch (Perca flavescens): A Study of Enzymes, Hepatocyte Metabolism, and Tissue Size

Abstract

This study analyzes the total potential of the liver in terms of enzyme activities and hepatocyteflux 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 gluconeogenesis. Lactate, alanine, and glycerolflux to glucose in isolated hepatocytes all decreased as a function of tissue DNA, as did alanine flux to CO₂. Again, no increases influx 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.