Changes in peptide hormones and liver enzymes in the rainbow trout deprived of food for 6 weeks

Abstract

The pancreatic peptide hormones insulin, glucagon, and glucagon-like peptide (GLP) modify metabolic flux in rainbow trout liver. This study quantifies the plasma titres of these peptide hormones using homologous radioimmunoassays after a 6-week fast and the coincident changes in specific enzymes in the liver. Fasting significantly changed a number of body parameters and depressed the plasma concentrations of each hormone, with the fall in insulin being the greatest and that in GLP the least. The relative hormone decline was such that the molar ratio of the glucagon-family peptides/insulin actually increased. Liver gluconeogenic enzymes were activated and pyruvate kinase underwent an apparent phosphorylation as indicated by altered kinetic parameters. These enzyme changes are evidence for an enhanced liver potential for gluconeogenesis during fasting. It is suggested that the changes in hormone molar ratios are responsible for the observed enzyme changes and are also key in the coordinated regulation of carbohydrate metabolism in the trout during fasting.