Liver phosphorylase activation during early phase of feeding behavior: a neurohumoral regulation

The mechanisms of liver glycogen depletion during the early phase of spontaneous feeding were examined in adult rats. A 40% increase in the activity of phosphorylase a, the active form of a key glycogenolytic enzyme, was detected 5 min after the onset of feeding, with a concomitant decrease of glycogen in the liver after 5 and 15 min. Within 60 min after the onset of feeding, the enzyme activity returned to the basal level and the glycogen content was restored. These metabolic responses were impaired by hepatic sympathetic denervation or by bilateral adrenodemedullation. It was concluded that the onset of meals may evoke an arousal of the sympathoadrenal system including the hepatic innervation, and that activation of this system is important in stimulating liver phosphorylase activity and glycogenolysis during the early phase of spontaneous feeding.