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Query: UMLS:C0038187 (starvation)
 24,951 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The effect of long-term starvation on glucagon-mediated hepatic glycogenolysis was investigated in the rat in vivo. Following glucagon (50 microgram/kg i.v.) fed rats showed rapid phosphorylase activation but no change in synthase-I activities. In contrast, rats fasted 72 hr (long-term fasting) showed rapid synthase inactivation but no significant phosphorylase activation. Rats fasted 24 hr (short-term fasting) demonstrated coordinated inactivation of synthase and activation of phosphorylase. Hepatic cyclic AMP responses were greater in fasted rats. Hepatic glycogen concentrations in rats fasted 72 hr were approximately 30% of fed levels. After glucagon, comparable decrements in hepatic glycogen and increments in plasma glucose concentrations were seen in fed and 72-hr groups. The diminished responsiveness of the hepatic phosphorylase system in rats fasted 72 hr was not attributable to altered cyclic AMP-dependent protein kinase or phosphorylase kinase activities. However, the diminished responsiveness could be ascribed to diminished total phosphorylase with nearly complete activation in the basal state. In fed and fasted rats, synthase decrements after glucagon correlated closely with basal levels of synthase-I. Thus, it is proposed that the enzymatic mechanism of glucagon-mediated hepatic glycogenolysis differs in fed and fasted rats. It is also proposed that partial hepatic glycogen reaccumulation during long-term fasting could be physiologically important for glucose homeostasis.
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PMID:Altered mechanism of glucagon-mediated hepatic glycogenolysis during long-term starvation in the rat. 21 68

Various hormonal and non-hormonal agents were tested for their ability to induce ornithine decarboxylase (EC 4.1.1.17) in primary cultures of fetal rat liver cells that retain many of the differentiated functions of hepatocytes. The only agents to induce ornithine decarboxylase in this cell type were fetal calf serum, prostaglandin E1 and cyclic AMP derivatives. Also, the amino acid arginine would induce ornithine decarboxylase in this cell type following arginine starvation for 24 h. These observations are in contrast to the wide range of hormones, e.g. insulin, hydrocortisone, glucagon and growth hormone, than can induce ornithine decarboxylase in vivo in the adult rat liver but which are all without effect on fetal rat liver cells.
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PMID:Factors regulating the induction of ornithine decarboxylase in fetal rat liver cells in culture. 21 27

When either fructose, glycerol, or succinate served as a sole source of carbon and energy in nitrogen-starved cultures of Escherichia coli W4597(K) the values of the kinetic constants of the equation that expresses the relationship between glycogen synthesis and hexose phosphates were different from the values observed when glucose was the sole source of carbon and energy. Addition of glucose during either exponential growth or nitrogen starvation to a culture using one of the other carbon sources slowed the rate of glycogen synthesis and shifted the values of the constants toward the values observed in cultures using glucose alone. Addition of cyclic AMP (cyclic adenosine 3':5'-monophosphate) during exponential growth of a culture using glucose caused the values of the constants to be shifted toward the values observed in cultures using a carbon source other than glucose. In all of the metabolic conditions studied in this report the adenylate energy charge ((ATP + 1/2 ADP)/(ATP + ADP + AMP)) and the level of the rate-limiting enzyme of glycogen synthesis, ADP-glucose synthetase (glucose 1-phosphate adenylyltransferase, EC 2.7.7.27), were the same. The data presented here indicate that the difference we observed in the quantitative relationship for glycogen synthesis is the result of the different cellular levels of cyclic AMP in the cells using glucose and the cells using one of the other carbon sources. Since cyclic AMP does not affect the velocity of ADP-glucose synthetase in vitro, apparently a change in the cellular level of cyclic AMP causes a shift in the cellular level of a presently unknown (and previously undetected) effector of this enzyme. The shift in the level of this effector evidently alters the response of the enzyme in vivo to the substrate glucose 1-phosphate and the activator fructose 1,6-diphosphate.
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PMID:Contribution of cyclic adenosine 3':5'-monophosphate to the regulation of bacterial glycogen synthesis in vivo. Effect of carbon source and cyclic adenosine 3':5'-monophosphate on the quantitative relationship between the rate of glycogen synthesis and the cellular concentrations of glucose 6-phosphate and fructose 1,6-diphosphate in Escherichia coli. 22 50

1. Glucokinase was absent from chicken liver and only the low Km hexokinases, inhibited by AMP, ADP but not ATP, were present. 2. The Km of chicken liver glucose-6-phosphatase for glucose-6-phosphate was reduced from 5.65 to 3.75 mM following starvation, and the enzyme was inhibited by glucose. 3. Starvation of chickens for 24 hr slightly lowered the hexokinase activity and doubled glucose-6-phosphatase activity; it did not change subcellular distribution of the enzymes. Oral glucose rapidly restored the activities to fed values. 4. It was concluded that glucose uptake into, and efflux from, chicken hepatocytes, was regulated by the activity and kinetic characteristics of glucose-6-phosphatase and by the glucose-6-phosphate concentration, and that the hexokinases had little regulatory function.
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PMID:Glucose phosphorylation and dephosphorylation in chicken liver. 23 87

Neuroblastoma cells were synchronized by a combined isoleucine plus glutamine starvation. Adenylate cyclase activity [ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1] was measured under basal conditions and in the presence of dopamine, adenosine and prostaglandin (PG) E1. A clear dissociation occurred between the respective evolution patterns of basal and agonist-stimulated adenylate cyclase activities. The magnitudes of the enzyme response to PGE1, adenosine, and dopamine also exhibited different evolution patterns during the cell cycle. Evolution of adenylate cyclase responsiveness to PGE1 during the cell cycle exhibited striking similarities with the intracellular 3':5'-cyclic AMP changes observed elsewhere. Use of theophylline and fluphenazine as specific inhibitors of adenosine and dopamine, respectively, made it possible to demonstrate that adenosine, dopamine, and PGE1 stimulated adenylate cyclase through independent receptor sites. Furthermore, whatever the stage of the cell cycle, responses to these three agonists were not additive, indicating that the receptors of adenosine, dopamine, and PGE1 control the same adenylate cyclase moieties. The data suggest that adenylate cyclase cell content and enzyme responsiveness to specific agonists can be independently controlled.
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PMID:Adenylate cyclase from synchronized neuroblastoma cells: responsiveness to prostaglandin E1, adenosine, and dopamine during the cell cycle. 26 97

The growth of the eucaryotic microorganism Dictyostelium discoideum in liquid culture was completely inhibited by the aspartic acid analog hadacidin (N-formylhydroxyamino-acetic acid). Growth arrest occurred both in chemically defined medium and in complex growth medium containing aspartic acid and AMP precursors such as adenine and adenosine. Although these compounds could not overcome the effect of hadacidin, growth was restored if cells were washed and resuspended in fresh growth medium. Additional experiments showed that D. discoideum contains adenylosuccinate synthetase, the enzyme which catalyzes the synthesis of adenylosuccinate from IMP, aspartic acid, and GTP in the de novo biosynthesis of purines. A partially purified preparation of this enzyme was obtained, and the effect of hadacidin on its activity was studied. We found that maximum inhibition of the D. discoideum activity occurs at a ratio of aspartic acid to hadacidin of 5:1, suggesting that the affinity of the drug for this enzyme is less than for the enzyme from rabbit muscle and plants but greater than for that from Escherichia coli. The effect of the drug can be overcome by a 10-fold excess of aspartic acid, suggesting that the drug acts as a competitive inhibitor. A comparison of the adenylosuccinate synthetase activity levels at various stages of growth showed that its specific activity decreases about 60% as cells enter the stationary growth phase, and decreases about 75% after starvation for 2 h. Further studies showed that in cells treated with hadacidin the rate of uptake of exogenous nutrients is reduced about 75% and that these cells are more resistant to rupture by osmotic shock. While the results of this study are consistent with the proposal that growth arrest is contingent upon inhibition of adenylosuccinate synthetase activity, they also suggest that, as a consequence of this inhibition, some physiological properties of the cell have been altered.
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PMID:Effect of hadacidin on growth and adenylosuccinate synthetase activity of Dictyostelium discoideum. 56 51

Methods are described for preparing and analyzing single preimplantation mouse embryos for a variety of metabolites and cofactors (glucose-6-P, fructose-6-P, fructose-1,6-bisphosphate, ATP, AMP, Pi, citrate, isocitrate, alpha-ketoglutarate, and malate). Oil-well and enzymatic cycling techniques are combined to provide the sensitivity needed to measure the amounts present (10(-12) to 1o(-15) moles). After experimental treatment, embryos are collected on glass slides and freeze-dried. They can then be stored indefinitely under vacuum at -25 degrees C without deterioration. With these procedures, the embryos were collected at successive stages of development and subjected to starvation and refeeding with glucose, pyruvate or both. The results confirm the existence of a block at early stages at the P-fructokinase step. This may be due to inhibition by the very high citrate levels present. The data suggest that glycolysis is turned on late in preimplantation development by the rise in fructose-6-P, a deinhibitor of P-fructokinase. In the citrate cycle, no step between citrate and alpha-ketoglutarate is rate-limiting, but a step between alpha-ketaglutarate and malate appears to impede the flux at early embryonic stages.
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PMID:Measurement of metabolites in single preimplantation embryos; a new means to study metabolic control in early embryos. 58 Feb 93

A system for in situ perfusion of rat hindquarters using a fluorocarbon for oxygen and CO2 exchange, and a polyol to provide oncotic pressure is described. Perfusion with glucose plus insulin resulted in no significant change in the tissue level of citrate cycle intermediates, phosphocreatine, ATP, ADP, AMP, and glycogen. Glucose was consumed at a linear rate, and lactate, pyruvate, alanine, glutamine, glutamate, and citrate were released into the perfusing medium. Inclusion of pyruvate resulted in elevation of citrate cycle intermediates and alanine, whereas acetate elevated the level of cycle intermediates without significant effect on tissue alanine or its release. Radioactivity from NaH[14C]O3 was incorporated into citrate cycle intermediates, glutamate, aspartate, and lactate by glucose-perfused hindquarters, the extent of which was markedly elevated as the tissue pyruvate was increased. When pyruvate was in the physiological range, acetate caused elevation in incorporation of CO2 into these metabolites, increased the concentration of citrate, and doubled the concentration of acetyl-CoA. Thirty-five to forty-four per cent of 14C incorporated into citrate was retained after enzymic degradation to 2-oxoglutarate. Perfusion with [2-14C-]propionate led to elevation in the level of citrate cycle intermediates, and radioactivity was incorporated into the latter, as well as glutamate, aspartate, lactate, pyruvate, alanine, and CO2. Two independent calculations estimated the rate of flux of 4-carbon cycle intermediates to 3-carbon metabolites of about 68 mumol/h (approximately 38 nmol/min/g of tissue), a rate in excess of those reported for alanine release from human or rat muscle during starvation. Arsenite blocked carbohydrate flux through the citrate cycle and effected accumulation of lactate, pyruvate, alanine, and 2-oxoglutarate. Flux from 4- to 3-carbon acids was diminished by arsenite, apparently as a result of lowered substrate concentration for decarboxylation. 3-Mercaptopicolinic acid, an inhibitor of phosphoenolpyruvate carboxykinase, was without effect on the parameters studied, suggesting that this enzyme is not involved in the decarboxylation reaction. It is concluded that (a) a constant level of citrate cycle intermediates is maintained in part by continuous flux of carbon into and out of the cycle by carboxylation and decarboxylation reactions; (b) the carbon skeleton of alanine released from skeletal muscle is derived in part from other amino acids which are catabolized to cycle intermediates; and (c) the subsequent removal of these intermediates is probably mediated by malic enzyme(s) (EC 1.1.1.40, or 1.1.1.36, or both.
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PMID:Carboxylation and decarboxylation reactions. Anaplerotic flux and removal of citrate cycle intermediates in skeletal muscle. 76 69

We suggest that two events are necessary for an asynchronous population of cells to undergo arrest in the GI phase of the cell cycle upon nutrient starvation. First, passage through GI must be prevented by a deficiency of some metabolic intermediate. Since this intermediate may act indirectly to arrest division, we designate it the "signal". We have found three conditions under which Saccharomyces cerevisiae cells arrest division in GI: sulfate starvation of a prototroph, methionine starvation of an auxotroph, or a shift of a conditional methionyl-tRNA synthetase mutant [L-methionine: tRNA Met ligase (AMP-forming), EC 6.1.1.10] to a restrictive condition. We interpret these results to indicate that the signal for sulfate starvation in S. cerevisiae is generated near the end of the sulfate assimilation pathway (at or beyond the formation of mehtionyl-tRNA). As a unifying hypothesis, we propose that the signal for all nutrients is generated at the level of protein biosynthesis.
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PMID:Control of cell division in Saccharomyces cerevisiae by methionyl-tRNA. 77 94

1. The regulation of the synthesis of phosphoenolpyruvate carboxykinase (GTP) (EC 4.1.1.32) in epididymal adipose tissue, liver and kidney in vivo was studied immunochemically. 2. Phosphoenolpyruvate carboxykinase (GTP) synthesis in adipose tissue is increased by starvation, diabetes and noradrenaline, and decreased by re-feeding and insulin. These changes were also seen in adrenalectomized rats and are qualitatively similar to those observed for the liver enzyme. This indicates the involvement of cyclic AMP as an inducer and insulin as a de-inducer in the regulation of phosphoenolpyruvate carboxykinase (GTP) in both tissues. (Induction and de-induction are defined as selective increase and decrease respectively in the rate of enzyme synthesis, regardless of the mechanism involved.)3. Adrenalectomy had little effect on phosphoenolpyruvate carboxykinase (GTP) synthesis in liver and kidney, but increased the synthesis rate of the adipose-tissue enzyme. Starvation and adrenalectomy had additive effects in increasing the synthesis rate of adipose-tissue phosphoenolpyruvate carboxykinase (GTP). In adrenalectomized diabetic rats glucocorticoids increased phosphoenolpyruvate carboxykinase (GTP) synthesis in liver and kidney while decreasing enzyme synthesis in adipose tissue. De-induction of adipose tissue phosphoenolpyruvate carboxykinase (GTP) is therefore regulated independently by glucocorticoids and insulin. 4. Although liver, kidney and adipose-tissue phosphoenolpyruvate carboxykinases (GTP) are seemingly identical, there is an apparent tissue-specific differentiation in regulatory systems for the enzyme.
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PMID:Regulation of phosphoenolpyruvate carboxykinase (GTP) in adipose tissue in vivo by glucocorticoids and insulin. 96 85


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