THE EFFECT OF THIOPENTAL ON HEPATIC GLYCOGEN PHOSPHORYLASE

¹ Departments of Anesthesiology and Pharmacology, School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania

The effect of thiopental on glycogen phosphorylase activity of liver and diaphragm was studied in vitro. Thiopental was found to cause an increase in active glycogen phosphorylase in liver but not in diaphragm. The thiopentalinduced increase in active phosphorylase in liver was additive with the stimulation produced by epinephrine. In diaphragm thiopental caused a potentiation of the epinephrine-induced increase in phosphorylase a even though the barbiturate alone caused no change. Pentobarbital also activated liver phosphorylase but was much less potent than thiopental.

The thiopental effect on liver phosphorylase was present in animals given reserpine and was not blocked by dichloroisoproterenol. This suggests that thiopental in stimulating phosphorylase acts by a nonadrenergic mechanism. Thiopental did not cause inhibition of phosphodiesterase-catalyzed hydrolysis of cyclic AMP and therefore does not appear to activate phosphorylase by a mechanism similar to that of the methylxanthines.