Dynamics of liver glycogen

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Abstract
Using histochemical techniques the glycogen content and the activities of glycogen synthetase (UDPGGT) and phosphorylase were studied in the livers of 106 golden hamsters under following experimental conditions: a) starvation of 16, 36, 48, 72 and 96 hours; b) alloxan-diabetes of 24, 48 and 72 hours; c) insulin-treatment (2 units, 30 min) after 24, 48 and 72 hours of alloxan diabetes. — Starvation leads to a depletion of liver glycogen during the first 48 hours, which is finally restricted to zone 3 of the liver acinus. After starvation of 72 and 96 hours a new glycogen accumulation is demonstrable in the microvasculatory periphery of the acinus (zone 3 and 2). The process of glycogen depletion is characterized in the beginning by a high phosphorylase activity in all zones of the acinus, later only in the forefield of glycogen content. The weak activity of glycogen synthetase is mainly restricted to zone 3. — All phases of glycogen depletion are to be found in alloxan diabetic animals, too. Out of 45 hamsters 23 showed an extreme depletion of glycogen; typical for this situation is a weak or absent glycogen synthetase activity in zone 3 and a broad field of phosphorylase activity in zones 1 and 2. The short stimulation by insulin leads to a considerable increase of glycogen synthetase activity at the portally oriented border of the glycogen area and to a shift of the moderate phosphorylase activity to zone 1. Thus the histochemical characteristics of glycogen depletion are: a shift of the reduced glycogen content in direction of the microvasculatory periphery of the liver acinus (zone 3), caused by a high phosphorylase activity in the portal forefield, while glycogen synthetase activity is low in the glycogen area. The histochemical characteristics of glycogen accumulation are: after a short phase of glycogen synthesis in all hepatocytes a moderate phosphorylase activity in zone 1 leads to a mobilization of the portal glycogen deposits and to an increasing accumulation of glycogen in the peripheral part of the acinus. At the portally oriented border of the glycogen area a high synthetase activity leads to a broadening of the glycogen area in direction of the portal branches. At the end of this process the “normal” pattern of the liver acinus occurs: all hepatocytes are filled with glycogen, the glycogen enzymes are restricted to the periportal border of zone 1.