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

1. Glycerol utilization by rat liver and kidney-cortex slices was studied in an attempt to define factors that might be important in the regulation of glycerol utilization by these tissues in vivo; the formation of glucose from glycerol by kidney-cortex slices was also studied. 2. The rate of glycerol uptake by liver slices was not changed (in comparison with the normal fed control) by starvation (48hr.), feeding with a low-carbohydrate diet (4-8 days) or feeding with a diet containing 25% glycerol (up to 18 days). Similarly, starvation or a low-carbohydrate diet had no effect on uptake by kidney-cortex slices; however, feeding with the glycerol diet increased glycerol uptake by kidney-cortex slices. 3. The rates of glycerol uptake by slices from both tissues were increased on raising the glycerol concentration from 0.2mm to 2.5 or 5.0mm. 4. Starvation increased the conversion of glycerol into glucose by kidney-cortex slices, but there was no effect of the low-carbohydrate diet; the rate of glucose formation was increased by feeding with the 25%-glycerol diet and was proportional to the increase in glycerol uptake. The rate of glucose production by these slices was increased by raising the glycerol concentration in the incubation medium from 0.2mm to 1.0mm, but, except for the slices from animals receiving the 25%-glycerol diet, there was no effect above 1.0mm-glycerol. 5. The significance of plasma glycerol concentration in regulating glycerol uptake by these tissues is discussed.
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PMID:The effects of dietary conditions and glycerol concentration on glycerol uptake by rat liver and kidney-cortex slices. 580 69

1. During the first two thirds of gestation, coinciding with a minimal accretion by the conceptus, the mother is in an anabolic state which is supported by her hyperphagia and the more efficient conservation of exogenous nutrients when she eats. During this phase maternal fat deposits are accumulated thanks to the enhancement in adipose tissue lipogenic and glycerologenic activity. In contrast, in the latter part of gestation, the rapid fetal growth is sustained by the intense transfer of nutrients from maternal circulation. 2. Glucose is quantitatively the most abundant of the several substrates that cross the placenta and despite increased maternal gluconeogenesis this transfer is responsible for the maternal tendency to hypoglycemia. This causes a switch to a net catabolic state which is especially evident in the net breakdown of fat depots. 3. Enhanced release of adipose tissue lipolytic products, free fatty acids (FFA) and glycerol, facilitates the liver synthesis of triglycerides and their later release into circulation associated to very low-density lipoprotein (VLDL). Glycerol is also used as an important gluconeogenic substrate and FFAs are broken down through beta-oxidation for ketone body synthesis. Flow through these pathways becomes increased when food is withheld and this actively contributes to the availability of fuels to the fetus which becomes partially preserved from maternal metabolic insult. Increased liver production of VLDL-triglycerides and decreased extrahepatic lipoprotein lipase contribute to exaggerated maternal hypertriglyceridemia which, besides being a floating metabolic reserve for emergency conditions such as starvation, constitutes an essential substrate for milk synthesis around parturition in preparation for lactation. 4. While the maternal anabolic tendencies found during the first two-thirds of gestation seem to be facilitated by hyperinsulinemia in the presence of a normal responsiveness to the hormone, it is proposed that most of the metabolic changes taking place during the last third of gestation seem to be caused by the insulin-resistant state which is consistently present at this stage, since its reversion caused by sustained exaggerated hyperinsulinemia also reverts several of these metabolic adaptations.
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PMID:Carbohydrate-lipid interactions during gestation and their control by insulin. 754 70

The contribution of glycerol to glucose production has been measured in healthy volunteers by the simultaneous primed constant infusion of 1-[13C]glycerol and 3-[3H]glucose and the determination of the rates of appearance (Ra) of glycerol, glucose, and glycerol-derived glucose. In the postabsorptive state, glycerol Ra was 3.11 +/- 0.44 mumol.kg-1.min-1, of which 36% was converted to glucose, accounting for 4.5% of total glucose production. After 62-86 h of starvation, glycerol Ra rose to 5.32 +/- 0.58 mumol.kg-1.min-1, and 68% of glycerol was converted to glucose. This accounted for 21.6% of total glucose production. Glycerol Ra was closely correlated with its conversion and contribution to glucose. These findings confirm that the contribution of glycerol to glucose production is directly correlated to its release as a consequence of lipolysis and support the notion that the central physiological role of accelerated lipolysis in fasting is the provision of gluconeogenic precursor.
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PMID:Glycerol gluconeogenesis in fasting humans. 764 79

The effects of glycerol on plant cell metabolism were studied with sycamore (Acer pseudoplatanus L.) cells using 31P nuclear magnetic resonance spectroscopy. After a long period of sucrose starvation, the addition of 50 mM glycerol to the medium did not restore the original glucose-6-P pool and led to a rapid accumulation of sn-glycerol-3-P in the cytoplasmic compartment. The synthesis of sn-glycerol-3-P was rapid and occurred first at the expense of cytoplasmic P(i). Accumulated sn-glycerol-3-P competitively inhibited glucose-6-phosphate isomerase activity when fructose-6-P was the varied substrate. Such a situation prevented the rapid recycling of triose phosphates back to hexose phosphates and led to an arrest of the functioning of the cytosolic and plastidial pentose phosphate pathways. Under these conditions, the flow of carbon to drive cell respiration derived almost exclusively from glycerol, and this polyalcohol was not used as a source of carbon skeletons for biosynthesis. Glycerol also induced the accumulation of O-phosphohomoserine in the cytoplasmic compartment as long as the cell culture medium contained sucrose. Finally glycerol added to sucrose-starved cells stopped the accumulation of phosphocholine (Roby, C., Martin J.-B., Bligny, R., and Douce, R. (1987) J. Biol. Chem. 262, 5000-5007) and prevented a further decline in the uncoupled rate of O2 consumption by the cells (Journet, E. P., Bligny, R., and Douce, R. (1986) J. Biol. Chem. 261, 3193-3199). These last observations strongly suggest that glycerol prevented the triggering of autophagy induced by sucrose starvation in sycamore cells.
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PMID:Multiple effects of glycerol on plant cell metabolism. Phosphorus-31 nuclear magnetic resonance studies. 806 74

The accumulation and excretion of polyols was investigated under various growth conditions and at different stages of the life cycle of Aspergillus niger. Glycerol was found to be the major solute in osmotic adjustment of the hyphae. Conidiospores contain large amounts of mannitol, which are rapidly metabolized during early germination, leading to the accumulation of glycerol. Glycerol is the major polyol in young mycelium, whereas in older mycelium mannitol and erythritol predominate. In all experiments, polyols were also excreted. The mechanism and function of this process is unknown, but it might be a way to control the levels of the intracellular polyol pools. Polyols are rapidly taken up again upon starvation. In a glycerol kinase mutant the synthesis of glycerol is unaffected but the excreted level of the polyol is higher. This glycerol is taken up again upon starvation, and accumulates intracellularly as it can not be metabolized further.
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PMID:Polyol pools in Aspergillus niger. 859 56

Mass isotopomer distribution analysis (MIDA) of glucose during infusion of [2-13C]glycerol is a new method for measuring total gluconeogenesis (GNG). Since this method relies on calculation of the isotopic enrichment (IE) of hepatic triose phosphates (TP), the results should be independent of the sites of tracer infusion and blood sampling. Postabsorptive and starved rats were infused with [2-13C]glycerol and sampled either in the arterial-venous (A-V) or venous-arterial (V-A) modes. Blood was also sampled from the portal vein. In both postabsorptive and starved rats, glycerol turnover rate (Rt) and the percent contribution of glycerol to total glucose production were higher in the A-V mode than in the V-A mode (P < .05). Glycerol IE in portal venous blood was intermediate between IE values observed in peripheral arterial and venous blood. Its use for calculating the contribution of glycerol to glucose production reconciled the results obtained with the two infusion-sampling modes in both postabsorptive and starved rats; this contribution was increased by starvation (P < .01). In postabsorptive rats, total GNG calculated from MIDA of glucose accounted for approximately 50% of glucose production whatever the infusion-sampling mode (A-V, 48.8% +/- 4.7%; V-A, 52.2% +/- 3.9%). This contribution increased to 90% in starved rats, again, with no difference between A-V (95.2% +/- 1.8%) and V-A (89.2% +/- 1.3%) modes. In conclusion, during infusion of [2-13C]glycerol, total GNG measured from MIDA of glucose is independent of the infusion-sampling mode, contrary to calculations of Rt and GNG from glycerol. Measurement of glycerol IE in portal venous blood reconciles the results obtained with the two modes with respect to the contribution of glycerol to GNG.
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PMID:Measuring glycerol turnover, gluconeogenesis from glycerol, and total gluconeogenesis with [2-13C] glycerol: role of the infusion-sampling mode. 869 28

The effects of nitrogen starvation on the anaerobic physiology of Saccharomyces cerevisiae were studied in cells cultivated in a bioreactor. The composition of the mineral medium was designed such that the nitrogen source became depleted while there was still ample glucose left in the medium. The culture was characterized by acoustic gas analysis, flow injection analysis and HPLC analysis of extracellular substrates and metabolites. During the cultivation, the macromolecular composition of the cells was analysed with respect to the cellular content of RNA, protein, trehalose and glycogen. During exponential growth under anaerobic conditions, the maximum specific growth rate conditions. Depletion of ammonium in the medium led to an abrupt decrease (mumax) of S. cerevisiae CBS 8066 (0.46 h-1) was identical to the mumax determined under aerobic in the flux through glycolysis. Subsequently, a continuous decrease in the carbon dioxide evolution rate, caused by catabolite inactivation of the hexose-transport system, was observed. The apparent half-life of the transport system under nitrogen starvation was 13 h. During the exponential growth phase, the cellular content of RNA and protein was 15% (w/w) and 60% (w/w), respectively. At the end of the cultivation where the cells had been starved of nitrogen for 18 h, the cellular content of RNA and protein had decreased to 4% (w/w) and 22% (w/w), respectively. The intracellular carbohydrate content increased dramatically as trehalose and glycogen accumulated to final concentrations of 7% (w/w) and 25% (w/w), respectively. Glycerol formation during nitrogen starvation was higher than that accounted for by the formation of organic acids, suggesting a protein turnover of approximately 6% h-1. The growth energetics of S. cerevisiae CBS 8066 also changed as a result of nitrogen starvation, and YxATP was observed to increase from 80 mmol g-1 during the exponential growth phase to more than 130 mmol g-1 towards the end of the cultivation. The presented results illustrate the effect of nitrogen starvation on glycerol formation, protein turnover, catabolite inactivation of the sugar-transport system, the cellular composition, the cell cycle and growth energetics.
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PMID:Physiological effects of nitrogen starvation in an anaerobic batch culture of Saccharomyces cerevisiae. 876 Sep 42

gamma-Glutamyl transpeptidase (GGT, EC 2.3.2.2.) catalyzes the transfer of the gamma-glutamyl moiety from gamma-glutamylcontaining compounds, notably glutathione (GSH), to acceptor amino acids and peptides. A second gene (GGTII) encoding GGT was previously isolated and characterized from the fission yeast Schizosaccharomyces pombe. In the present work, the GGTII-lacZ fusion gene was constructed and used to study the transcriptional regulation of the S. pombe GGTII gene. The synthesis of beta-galactosidase from the GGTII-lacZ fusion gene was significantly enhanced by NO-generating SNP and hydrogen peroxide in the wildtype yeast cells. The GGTII mRNA level was increased in the wild-type S. pombe cells treated with SNP. However, the induction by SNP was abolished in the Pap1-negative S. pombe cells, implying that the induction by SNP of GGTII is mediated by Pap1. Fermentable carbon sources, such as glucose (at low concentrations), lactose and sucrose, as a sole carbon source, enhanced the synthesis of beta-galactosidase from the GGTII-lacZ fusion gene in wildtype KP1 cells but not in Pap1-negative cells. Glycerol, a non-fermentable carbon source, was also able to induce the synthesis of beta-galactosidase from the fusion gene, but other non-fermentable carbon sources such as acetate and ethanol were not. Transcriptional induction of the GGTII gene by fermentable carbon sources was also confirmed by increased GGTII mRNA levels in the yeast cells grown with them. Nitrogen starvation was also able to induce the synthesis of beta-galactosidase from the GGTII-lacZ fusiongene in a Pap1-dependent manner. On the basis of the results, it is concluded that the S. pombe GGTII gene is regulated by oxidative and metabolic stress.
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PMID:The gene encoding gamma-glutamyl transpeptidase II in the fission yeast is regulated by oxidative and metabolic stress. 1620 43

Net degradation of cellular components occurs in plant cells cultured under starvation conditions, and autophagy contributes to the degradation of intracellular proteins. In this study, we investigated the degradation of membrane phospholipids by autophagy in cultured tobacco (Nicotiana tabacum) cells. The amounts of total phospholipids and a major phospholipid, phosphatidylcholine (PC), decreased, whereas phosphorylcholine, a degradation product of PC, increased in response to deprivation of sucrose. The addition of glycerol to the culture medium inhibited both the degradation of phospholipids and the concomitant increase of phosphorylcholine. Glycerol, however, did not block autophagy, which was assessed by the accumulation of autolysosomes in the presence of a cysteine protease inhibitor. On the other hand, 3-methyladenine, an inhibitor of autophagy, did not affect the net degradation of PC. We labeled intracellular phospholipids by loading cells with a fluorochrome-labeled fatty acid and chased it under sucrose-free conditions. Glycerol slowed down the decrease in the amount of fluorochrome-labeled PC, suggesting that it inhibits the degradation process of PC. These results show that phospholipids are degraded by mechanisms different from autophagy in tobacco cells cultured under sucrose-free conditions.
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PMID:Autophagy is not a main contributor to the degradation of phospholipids in tobacco cells cultured under sucrose starvation conditions. 1644 32

The effect of calorie restriction (CR) on life span extension, demonstrated in organisms ranging from yeast to mice, may involve the down-regulation of pathways, including Tor, Akt, and Ras. Here, we present data suggesting that yeast Tor1 and Sch9 (a homolog of the mammalian kinases Akt and S6K) is a central component of a network that controls a common set of genes implicated in a metabolic switch from the TCA cycle and respiration to glycolysis and glycerol biosynthesis. During chronological survival, mutants lacking SCH9 depleted extracellular ethanol and reduced stored lipids, but synthesized and released glycerol. Deletion of the glycerol biosynthesis genes GPD1, GPD2, or RHR2, among the most up-regulated in long-lived sch9Delta, tor1Delta, and ras2Delta mutants, was sufficient to reverse chronological life span extension in sch9Delta mutants, suggesting that glycerol production, in addition to the regulation of stress resistance systems, optimizes life span extension. Glycerol, unlike glucose or ethanol, did not adversely affect the life span extension induced by calorie restriction or starvation, suggesting that carbon source substitution may represent an alternative to calorie restriction as a strategy to delay aging.
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PMID:Tor1/Sch9-regulated carbon source substitution is as effective as calorie restriction in life span extension. 1942 15


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