Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0038187 (starvation)
 24,951 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Glycogen synthase I (UDP glucose: glycogen alpha-4-glycosyltransferase, EC2.4.1.11) of the tapeworm Hymenolepis diminuta is the form of the enzyme which is active in vivo, while the D-form represents an inactive "storage form." Utilizing the differential effect of inorganic phosphate (Pi) on the I and D-forms, the ratio of the 2 forms in vivo has been determined under conditions of starvation of the host and refeeding of the parasite with glucose. This procedure reveals that conversion of the inactive D-form to the active I-form takes place when glycogen-depleted worms are incubated in glucose. The activity of glycogen synthase I also is affected by the molecular weight of the primer glycogen. With certain molecular weight fractions, enzymatic activity is higher than with others. This specificity of the glycogen primer could explain the relatively low concentrations of those molecular weight fractions which confer the highest synthase activity.
 ...
PMID:Glycogen synthase of Hymenolepis diminuta. II. Nutritional state, interconversion of forms, and primer glycogen molecular weight as control factors. 10 7

The effects of starvation on the hepatic glycogen synthase and phosphporylase systems were sequentially assessed in fed and 24-120-hr-fasted rats. Enzymic changes before and after glucose were correlated with simultaneous measurements of hepatic cyclic AMP and glycogen concentrations and glucose, insulin, and glucagon concentrations in the portal vein plasma. Fasting caused parallel changes in plasma glucose and hepatic glycogen concentrations with decreases by 24 hr and subsequent increases, which correlated with increases in hepatic synthase l and decreases in phosphorylase activites. Hepatic cyclic AMP levels increased as 24-48 hr, decreased below fed levels at 96 hr, and increased again at 120 hr. Fasting caused progressive impairment of glucose disposal, decreased basal and postglucose insulin concentrations, and decreased basal glucagon levels at 48-72 hr. Hepatic synthase l increments following glucose were exaggerated in 48-120-hr-fasted rats, although consistent phosphorylase decrements were seen only in fed rats. There was no clearcut relationship between synthase activation and phosphorylase inactivation following glucose in fed or fasted rats.
 ...
PMID:Effect of starvation on hepatic glycogen metabolism and glucose homeostasis. 20 23

The glycogen content of cultured chick embryo breast muscle cells changes during their development and can be reduced by starvation. It is demonstrated that the rate of glucose incorporation into glycogen and the degree of interconversion of glycogen synthase are controlled by the actual glycogen content. Stimulation of both corresponding activities by insulin is found in fused and in unfused cells. The insulin response depends on the extracellular calcium concentration and can be mimicked by the ionophore A 23187. These metabolic effects as well as calcium efflux data confirm the hypothesis that insulin acts on its enzyme target via increased cytoplasmic calcium concentration. Cytochalasin B is shown to inhibit the interconversion but does not interfere with the insulin-induced increase of the mitochondrial calcium pool or with the acceleration of the calcium efflux out of 45C-preloaded myotubes.
 ...
PMID:Regulation of glycogen synthase interconversion in cultured muscle cells: actions of insulin, calcium, ionophore A 23187 and cytochalasin B. 40 13

We have studied the changes in concentration of glycogen, glucose and the bisphosphorylated sugars, glucose 1,6-P2 and fructose 2,6-P2, in several rat brain regions during 72 h of starvation. The animals were killed by focused microwave irradiation. The activities of glycogen metabolizing enzymes in the different areas were measured. A large decrease in glycogen and glucose concentration was observed in all areas. The concentrations of bisphosphorylated sugars changed, suggesting that an increase in glycolysis could take place at the beginning of starvation, with blood glucose as a major energy source. Differences in metabolite concentration before starvation disappeared after 72 h. The activities of glycogen synthase, glycogen phosphorylase and glycogen phosphorylase kinase were similar in all areas, and they did not change during starvation.
 ...
PMID:Effect of starvation on glycogen and glucose metabolism in different areas of the rat brain. 144 41

In isolated hepatocytes from 24 h-starved rats, no glycogen synthesis was observed in the presence of glutamine. By contrast, glutamine was the best gluconeogenic substrate to induce glycogen synthesis in isolated hepatocytes from 72 h-starved rats. The effect of glutamine on glycogen synthesis was not accompanied by parallel changes in glucose or lactate production. Glutamine activated glycogen synthase independently of the starvation period; however, the extent of synthase activation was 2-fold higher in isolated hepatocytes from 72 h-starved rats than in hepatocytes from 24 h-starved rats. This increase in synthase activation was associated with increased cell swelling. The rate of glutamine transport was not significantly different in hepatocytes from 24 h- and 72 h-starved rats. By contrast, the intracellular glutamate concentration was 1.5-fold higher after 3 days of starvation in hepatocytes incubated with 5 mM-glutamine. We propose that glutamine may play a key role in the glycogen synthesis observed in vivo after 3 days of starvation.
 ...
PMID:Glutamine is a good substrate for glycogen synthesis in isolated hepatocytes from 72 h-starved rats, but not from 24 h- or 48 h-starved rats. 147 95

The responses of hepatic glycogen synthase and phosphorylase to fasting and refeeding were assessed as part of an investigation into possible sites of insulin resistance in gold thioglucose (GTG) obese mice. The active forms glycogen synthase and phosphorylase (synthase I and phosphorylase a) and the total activity of these enzymes were estimated in lean and GTG mice over 48 h of food deprivation, and for 120 min after glucose gavage (1 g/kg wt). In lean mice there was a maximal reduction in hepatic glycogen content after 12 h of starvation and the activity of phosphorylase a decreased from 23.8 +/- 1.9 to 6.8 +/- 0.7 mumol/g protein/min. These changes were accompanied by an increase in the activity of synthase I (from 0.14 +/- 0.01 to 0.46 +/- 0.04 mumol/g protein/min). In obese mice, similar changes in enzyme activity occurred after 48 h of starvation. These changes were accompanied by a significant reduction in the hyperinsulinemia and hyperglycemia of the GTG mice. After glucose gavage in both lean and obese mice, the activity of synthase I further increased over the first 30 min and declined thereafter. The activity of phosphorylase a increased progressively after refeeding. Results from this study suggest that despite increased hepatic glycogen deposition, the responses of glycogen synthase and phosphorylase, in livers of obese mice, to fasting and refeeding are similar to those of control mice even in the presence of insulin resistance.
 ...
PMID:The effects of fasting and refeeding on liver glycogen synthase and phosphorylase in obese and lean mice. 160 90

Glucose homeostasis and fatty acid metabolism are abnormal in patients with cirrhosis. To assess the metabolic response to starvation in an animal model of cirrhosis, glycogen and fuel metabolism were characterized in rats with CCl4-induced cirrhosis studied 2 wk after 10 weekly doses of CCl4. Plasma concentrations of glucose and beta-hydroxybutyrate were not different between fed CCl4-treated and control rats, but plasma nonesterified fatty acid concentrations were higher in cirrhotic animals (0.25 +/- 0.01 vs. 0.39 +/- 0.04 mmol/L; p less than 0.05). After 12 hr of starvation, the plasma nonesterified fatty acid concentration had reached 0.58 +/- 0.04 mmol/L in CCl4-treated rats, compared with 0.38 +/- 0.04 mmol/L in control rats (p less than 0.05). The redistribution of the hepatic carnitine pool toward acylcarnitines, which is characteristic of starvation, was complete after fasting for 12 hr in the CCl4-treated rats, compared with the 24 hr required in control rats. In fed cirrhotic rats, liver glycogen content per gram liver was decreased by 64% compared with control rats (30.0 +/- 5.1 vs. 10.8 +/- 1.1 mg/gm liver wet wt; p less than 0.05). After 12-hr fasting, hepatic glycogen content had fallen to 14.3 +/- 3.9 and 4.8 +/- 0.4 mg/gm liver wet wt (p less than 0.05) in control and cirrhotic animals, respectively. To further characterize the status of glycogen metabolism in cirrhotic livers, activities of glycogen synthase and glycogen phosphorylase were determined. Hepatic active and total glycogen phosphorylase activities normalized to hepatocellular content were unaffected by CCl4 treatment, whereas total glycogen synthase activity was increased by 45%.(ABSTRACT TRUNCATED AT 250 WORDS)
 ...
PMID:Decreased hepatic glycogen content and accelerated response to starvation in rats with carbon tetrachloride-induced cirrhosis. 195 69

Skeletal muscle glycogen content and structure, and the activities of several enzymes of glycogen metabolism are reported for the hepatic glycogen phosphorylase b kinase deficient (gsd/gsd) rat. The skeletal muscle glycogen content of the fed gsd/gsd rat is 0.50 +/- 0.11% tissue wet weight, and after 40 hours of starvation this value is lowered 40% to 0.30 +/- 0.05% tissue wet weight. In contrast the gsd/gsd rat liver has an elevated glycogen content which remains high after starvation. The skeletal muscle phosphorylase b kinase, glycogen phosphorylase, glycogen synthase and acid alpha-glucosidase activities are 17.2 +/- 2.9 units/g tissue, 119.9 +/- 6.4 units/g tissue, 12.2 +/- 0.4 units/g tissue and 1.4 +/- 0.4 milliunits/g tissue, respectively, with approx. 20% of phosphorylase and approx. 24% of synthase in the active form (at rest). These enzyme activities resemble those of Wistar skeletal muscle, and again this contrasts with the situation in the liver where there are marked differences between the Wistar and the gsd/gsd rat. Fine structural analysis of the purified glycogen showed resemblance to other glycogens in branching pattern. Analysis of the molecular weight distribution of the purified glycogen indicated polydispersity with approx. 66% of the glycogen having a molecular weight of less than 250 X 10(6) daltons and approx. 25% greater than 500 X 10(6) daltons. This molecular weight distribution resembles those of purified Wistar liver and skeletal muscle glycogens and differs from that of the gsd/gsd liver glycogen which has an increased proportion of the low molecular weight material.(ABSTRACT TRUNCATED AT 250 WORDS)
 ...
PMID:Skeletal muscle glycogen content, structure, and metabolism are normal in rats with hepatic glycogen phosphorylase kinase deficiency. 263 61

Rats were fed a 70% carbohydrate, 70% protein, 70% fat, or a standard purified diet for 7 d to determine the effect of the diet on heart glycogen synthase response to an acute insulin challenge. Rats fed the high protein or the high fat diets, i.e., the carbohydrate-free diets, exhibited insulin resistance as evidenced by higher plasma glucose levels following insulin administration when compared to rats fed high carbohydrate or standard diet. The diets had no effect on the initial proportion of synthase in the active or I form. Insulin injection resulted in an increase in the proportion of synthase in the active form in rats fed the standard, high carbohydrate or high protein diets, but not in rats fed the high fat diet. Synthase phosphatase activity was similar in rats fed one of the four diets compared to rats fed a nonpurified diet. Thus the lack of synthase response to insulin in fat-fed rats was not due to diminished synthase phosphatase activity. Neither the diets nor insulin administration had any effect on the proportion of phosphorylase in the active or a form. Cardiac glycogen was significantly lower in rats fed the high fat diet than in those fed the standard diet. The latter was a surprising observation since the high fat diet was used to simulate a starved state and cardiac glycogen concentrations increase with starvation.
 ...
PMID:Effect of insulin administration on cardiac glycogen synthase and synthase phosphatase activity in rats fed diets high in protein, fat or carbohydrate. 298

Investigations in our laboratory have shown that the activity of glycogen synthase phosphatase in the liver is shared by at least two functionally distinct proteins: a G-component, which is tightly associated with glycogen particles, and a soluble S-component. Most preparations of glycogen synthase-b that are isolated from the liver of fed glucagon-treated animals require the presence of both components in order to be converted to synthase-a. The G-component is subject to control mechanisms that do not affect the S-component. Its activity is strongly inhibited by phosphorylase-a. This feature explains why glycogen synthesis and glycogenolysis do not normally occur simultaneously, except in the glycogen-depleted liver, where a futile cycle may occur. Experiments in vitro have shown that a minimal glycogen concentration is required to ensure the interaction between the G-component and phosphorylase-a. The G-component is also selectively inhibited by Ca2+, and the magnitude of this inhibition depends markedly on the glycogen concentration. The latter inhibition is probably one of the mechanisms by which cyclic adenosine monophosphate (cAMP)-independent glycogenolytic agents achieve the inactivation of glycogen synthase in the liver. Glucocorticoid hormones and insulin are required for the induction and/or maintenance of the G-component in the liver. During the development of the fetal rat, glucocorticoids induce the G-component in the liver. This is an essential event in the glucocorticoid-triggered deposition of glycogen in the fetal liver. A functional adrenal cortex is also required in the adult animal to prevent a loss of the capacity for hepatic glycogen storage during starvation. The latter capacity depends on the concentration of functional G-component in the liver. Chronic diabetes causes a similar functional loss. However, the effect of glucocorticoids is not mediated by a putative secretion of insulin.
 ...
PMID:Control of glycogen synthesis in health and disease. 303 40


1 2 3 4 5 6 Next >>