Starvation and the metabolism of hepatocytes isolated from the American eel,Anguilla rostrata LeSeur

Summary

Gluconeogenic, lipogenic, glycogenic and oxidative rates were estimated from¹⁴C-lactate,¹⁴C-alanine and¹⁴C-aspartate using a hepatocyte preparation isolated from starved immature American eels,Anguilla rostrata. Lactate gluconeogenesis increased significantly during starvation at 5 and 15°C. Alanine gluconeogenesis generally decreased during starvation. At the 2nd month of the starvation at 5 and 15°C, and the 8th month of starvation at 15°C, however, alanine gluconeogenesis was significantly higher than in the fed control. These increases in alanine gluconeogenesis occurred during a period of high glucose demand. Aspartate gluconeogenesis was quantitatively minor when compared to the other two substrates. Glycerol synthesis and esterification from the three substrates increased until the 5th month at 5 and 15°C followed by a gradual decline thereafter. Significant increases in glycogen synthesis occurred between the 3rd and the 5th months at 15°C, but rates were small compared to glucose synthesis. Rates of substrate oxidation appeared sufficient to provide adequate ATP to sustain gluconeogenesis in both the fed and starved eel hepatocyte. Glucagon stimulated lactate gluconeogenesis, but not amino acid gluconeogenesis in late starved eel hepatyocytes. Major changes in metabolite concentrations that occurred during starvation were increases in plasma glucose and amino acids; a significant liver glycogen depletion at the 2nd month followed by a return to control values at the third month; and, a significant protein depletion in white skeletal muscle at the 3rd month. These data suggest that lactate glucogeogenesis, but not amino acid gluconeogenesis or glycogenolysis, is the major source of tissue carbohydrates during eel starvation.