Mammalian liver glycogen synthetase. Altered primer requirements in the presence of glucose 6-phosphate or orthophosphate.
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The adenosine kinase inhibitor 5-iodotubercidin (Itu) was found to have the following effects on glycogen metabolism in hepatocytes of fasted rats. (1) Itu strongly stimulated glycogen synthesis from different substrates (glucose, lactate plus pyruvate, dihydroxyacetone, glycerol and fructose). In cells incubated with these substrates, the well-known stimulating effect of amino acids and that of Itu was more than additive. (2) In parallel with the increase in glycogen deposition, there was an increase in synthase a and a decrease in phosphorylase a concentrations after administration of Itu. Synthase a was increased by Itu and amino acids in an additive manner, whereas the observed activation of phosphorylase after addition of amino acids was antagonized by Itu. (3) In contrast with amino acids, Itu increased neither the cell volume nor the aspartate and glutamate concentrations. (4) Itu enhanced the levels of cyclic AMP. The stimulation of glycogen deposition in the presence of Itu persisted when the cyclic AMP concentration was further increased by adenosine or 2-chloroadenosine. (5) Itu decreased the concentration of ATP, but its effects on glycogen synthesis, synthase a and phosphorylase a concentrations persisted when the ATP catabolism was prevented by adenosine. (6) The effect of Itu on glycogen synthesis was not the result of inhibition of adenosine kinase, since 5'-amino-5'-deoxyadenosine, another inhibitor of this enzyme, had no effect on glycogen deposition.
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Ground-glass hepatocytes have been described in Lafora's disease, fibrinogen deposition, hepatitis B, type IV glycogenosis, and alcohol aversion (cyanamide) therapy. We encountered ground-glass hepatocytes with intracytoplasmic inclusions in four liver biopsies from three transplanted patients who had none of the above-mentioned underlying diseases. One patient was a 4-year-old boy who had a kidney transplant for severe ureterovesical reflux. Patient 2 was a 52-year-old man who had two liver transplants because of hepatitis C. The third patient was a 7-month-old girl who underwent a multivisceral transplant because of necrotizing enterocolitis and liver failure induced by total parenteral nutrition. The patients developed liver abnormalities from 45 days to 4 years after their transplants. The livers showed conspicuous ground-glass hepatocytes in 90% of the children's samples and 30% of the adult liver cells. The cytoplasmic bodies stained strongly for Gomori methenamine-silver; they were positive for periodic acid-Schiff without diastase, but negative after diastase digestion. They were negative for colloidal iron and hepatitis B core and surface antigens. Electron microscopy revealed non-membrane bound aggregates of glycogen. Idiopathic ground-glass hepatocytes occur in transplanted patients and represent accumulation of altered glycogen. However, their clinical significance and cause are not entirely elucidated.
Lean and genetically obese (fa/fa) rats were fed ad libitum, or fasted for 17 h and then meal-fed for varying time intervals. During refeeding, glucose-6-phosphatase activity of lean rats declined to the low value that was present in livers of fasted obese rats and which remained unchanged in the obese group during the meal. Refeeding also resulted in increases in hepatic concentrations of glucose-6-phosphate and fructose-6-phosphate, fructose 1,6-bisphosphate, fructose-2,6-bisphosphate, alpha-glycerophosphate, pyruvate and lactate in lean and obese rats, absolute values being higher in the fasted obese than in the fasted lean group. Obese animals had higher postprandial portal blood insulin, glucose and lactate concentrations than lean animals. In spite of this, the rate of hepatic glycogen deposition was the same in both groups and was accompanied by similar glycogen synthase a levels. Following refeeding, phosphorylase was transiently inactivated in livers of lean but not of obese animals, while glycogen synthase was inactivated in both groups. The data suggest that in lean animals refeeding was associated with a stimulation of liver glycolysis, presumably by insulin; in fasted obese rats hepatic glycolysis was already in a stimulated state and was only slightly enhanced further after the meal, in keeping with their unaltered hyperinsulinaemia; there was an increased turnover of liver glycogen or a resistance to insulin stimulation of glycogen synthesis in fa/fa rats during refeeding.