Hormonal Control of Glycogenolysis and Gluconeogenesis in Isolated Rat Liver Cells

TLDR

The study investigated carbohydrate metabolism in isolated rat liver parenchymal cells. Isolated rat liver cells from fed and fasted rats showed glycogenolysis and gluconeogenesis rates similar to intact livers, with glucagon, epinephrine, or cyclic nucleotides stimulating glycogen breakdown by about 220–250% and glucose synthesis from lactate, pyruvate, alanine, fructose, and dihydroxyacetone, whereas fasted cells could not use glutamate, aspartate, or citric‑acid‑cycle intermediates.

Abstract

Abstract The carbohydrate metabolism of isolated rat liver parenchymal cells was investigated. Cells isolated from fed rats retained glycogen and released glucose into the suspending medium at a rate of about 25 µg of glucose per mg of cell protein per hour. Glucagon, epinephrine, or cyclic nucleotides stimulated glycogenolysis about 220 to 250%. Cells isolated from rats fasted 18 to 24 hours synthesized glucose from lactate, pyruvate, alanine, glycerol, dihydroxyacetone, and fructose, but not from glutamate, aspartate, or citric acid cycle intermediates. The rates of gluconeogenesis by the liver cells from all substrates tested were comparable to those measured in intact, perfused livers. Glucagon, epinephrine, or cyclic nucleotides stimulated glucose synthesis from lactate, pyruvate, alanine, fructose, and dihydroxyacetone, but not from other substrates. The basal levels of cyclic adenosine 3':5'-monophosphate in fed and fasted cells were similar to those reported for intact liver. Time course experiments with the cells showed that glucagon increased the levels of cyclic adenosine 3':5'-monophosphate within 30 s, and that measurable increases in glycogenolysis or gluconeogenesis from lactate occurred within 2 to 4 min. The results suggest that the carbohydrate metabolism of the isolated liver cells closely resembles that of the intact, perfused liver.