Effect of feeding and fasting on the early steps of glucagon action in isolated rat liver cells.

The effect of the nutritional state (fasted or fed) on the binding of glucagon and on the glucagon-stimulated cyclic AMP accumulation in the presence of theophylline was studied in isolated rat liver cells. The binding of glucagon was higher in cells from fed than in those from fasted rats at each concentration of glucagon tested between 0.1 and 36 nM. The specific binding of the hormone was about 2-fold higher in cells from fed than from fasted rats. At concentrations of glucagon between 0.1 and 2.2 nM, the accumulation of cyclic AMP in the presence of 1 mM theophylline was higher in the cells from fed rats. Furthermore, 4 times as much glucagon was required to elicit half-maximal cyclic AMP accumulation in the cells of fasted (1.47 nM) than in the cells of fed (0.35 nM) rats. These data suggest that, in isolated rat liver cells, both glucagon binding to receptor sites and glucagon-stimulated cyclic AMP levels in the presence of theophylline can be affected by the nutritional status of the animal.