Metabolism of hexose phosphate esters. 1. Metabolism in normal and alloxan-diabetic rabbits. 2. Metabolism in isolated rat diaphragm and the influence of insulin

Abstract

Hexose phosphates can penetrate into tissue cells of rabbits, and evidence is advanced that they are metabolized within the cells. In contrast to the behavior of glucose, intraven. injected glucose- 1-phosphate and glucose-6-phosphate disappeared rapidly from the blood of both normal and alloxan-diabetic rabbits; a subsequent increase in blood glucose and in the inorganic P of the blood and urine was observed. Approx. 30% of the injected glucose-1-phosphate was recovered in the urine of both normal and alloxan-diabetic rabbits and 40 and 55% of the injected glucose-6-phosphate in the urine of normal and diabetic rabbits, respectively. In the presence of isolated rat diaphragm muscle, uptake of glucose-1-phosphate from the medium was higher than that of glucose. Addition of insulin increased the glucose uptake and inhibited uptake of glucose-1-phosphate. The amt. of glycogen synthesis by rat diaphragm muscle was of the same order in systems containing glucose-l-phosphate (2%) and systems containing glucose (2%), and in both cases was largely dependent on the initial glycogen content of the muscle. Insulin increased the glycogen synthesis from glucose but had no effect on glycogen synthesis from glucose-1-phosphate. O2 consumption of isolated rat diaphragm was increased by the addition of glucose-1-phosphate (2%) and unaffected by glucose. When 2,4-dinitrophenol (4.83 x 10-5 M) was added to the medium, O2 consumption increased in the presence of glucose and was inhibited in the presence of glucose-1-phosphate. Glucose 6-phosphate and fructose 6-phosphate were acted on by an isomerase enzyme present in rat diaphragm muscle forming an equilibrium mixture containing approx. 40% fructose 6-phosphate and 60% glucose 6-phosphate. Rat diaphragm muscle incubated in this equilibrium mixture did not synthesize glycogen nor was its O2 consumption affected.