Metabolic organization of liver during spawning migration of sockeye salmon

Although earlier studies have established broad outlines of biochemical changes during salmon spawning migration, the metabolic organization of specific organs has hitherto remained unknown. In this study, we assessed the performance of isolated liver cells from anorexic female sockeye salmon (Oncorhynchus nerka) at four sampling sites along their 1,150-km spawning migration. Isolated hepatocytes maintain high rates of gluconeogenesis and CO2 release from amino acids and lactate throughout the migration. Alanine, derived from proteolysis of white muscle, constitutes the single most important source for de novo synthesis of glucose. Just before spawning, when glycogen reserves reach a maximum, gluconeogenesis from alanine is specifically inhibited, whereas its conversion to CO2 and the utilization of other substrates are relatively unchanged. Spawning, apparently supported by carbohydrate catabolism, is accompanied by depletion of glycogen reserves from muscle as well as liver and a stimulation of gluconeogenesis from amino acids. At the onset of migration, palmitate oxidation accounts for about half the CO2 released by liver cells; its contribution decreases during the migration and is negligible after spawning.