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At least 325 records · Page 18Linked to original sources
PubMed1997

Stimulatory effect of progesterone and 5 beta-progesterone on lipid synthesis in hamster flank organs.

In order to study lipid synthesis in female hamster flank organs during the estrous cycle, glands were obtained from different animals during different phases of the cycle. Lipid metabolism of [U-14C]glucose was studied under in vitro conditions. The radioactive lipids formed, were extracted from the glands and quantified. An aliquot of the extract was submitted to TLC to isolate and identify the lipids formed. Lipid synthesis in the glands increased significantly during estrous compared with the diestrous phase, suggesting the influence of sex hormones on lipid metabolism in flank organs. The radioactive lipids isolated and identified were: phospholipids, cholesterol, glycerides, waxes, and cholesterol esters. The percentages of conversation from [U-14C]glucose to cholesterol esters were minor in extracts from glands of diestrous animals as compared to estrous and proestrous animals, whereas glycerides and waxes increased significantly in metestrous and diestrous animals. To verify and evaluate the role of estrogen and progesterone in lipid synthesis, three different groups of gonadectomized female hamsters were injected daily with estradiol, progesterone, and 5 alpha-progesterone. After treatments, glands were incubated with [U-14C]glucose to determine the incorporation of radioactive glucose into lipids under culture conditions. The radioactive lipids synthesized were subsequently extracted and identified. The results showed that estrogen had no effect on in vitro [U-14C]glucose incorporation into lipids by flank organs, compared to the vehicle, whereas progesterone and 5 alpha-progesterone increased radioactive lipid synthesis by the glands significantly (p < 0.05). The radioactive lipids isolated and identified from extracts of gonadectomized female hamster flank organs were: phospholipids, cholesterol, triglycerides, waxes, and cholesterol esters. Gonadectomy increased phospholipid synthesis and decreased that of monoglycerides, diglycerides, and waxes. The percentages of conversion from [U-14C]glucose to cholesterol esters were higher after progesterone and 5 alpha-progesterone treatments than in vehicle and estrogen-treatments. Our data indicate that progesterone and 5 alpha-progesterone-treatments increased the in vitro [U-14C]glucose incorporation into lipids in flank organs from gonadectomized female hamsters. Furthermore, the major lipid synthesized by glands under these stimuli were cholesterol fatty acids. Thus, progesterone and 5 alpha-progesterone alter the consistency of sebum from gonadectomized female glands.

Animals↗
PubMed1989

Isocratic high-performance liquid chromatographic determination of the concentration and specific radioactivity of phosphoenolpyruvate and uridine diphosphate glucose in tissue extracts.

A rapid and efficient isocratic high-performance liquid chromatographic method for studying the metabolism of phosphoenolpyruvate and uridine diphosphate glucose (UDPG) has been developed. For each compound this method can measure tissue concentrations in the range 0.1-1000 nmol/g of tissue and determine specific radioactivity. All measurements can be performed in 200 mg of tissue. The recoveries of uridine diphosphate [6-3H]glucose and phosphoenol[1-14C]pyruvate from liver tissue homogenates were 97 and 99%, respectively. Following intra-arterial infusion of [6-3H]glucose and [U-14C]lactate in conscious rat, the concentration and specific radioactivity of phosphoenolpyruvate and UDPG were determined in rat liver. The method may be applied to experimentation in small animals using radiolabelled precursors in order to quantitate in vivo the glycogenic and gluconeogenic fluxes.

Animals↗
PubMed1986

Kinetics of ascorbate transport by cultured retinal capillary pericytes. Inhibition by glucose.

Accumulation of radioactive L-[carboxyl-14C]-ascorbic acid by cultured bovine retinal capillary pericytes was studied. Kinetic analysis of the transport showed a time-dependent, saturable system with an apparent Km of 76.0 microM and a Vmax of 42 pmole/micrograms DNA/min. A facilitated carrier diffusion process was established on the basis that the system was not sensitive to 2,4-dinitrophenol, ouabain, or reduced sodium concentration in the incubation media, and that the carrier system demonstrated stereospecificity for an ascorbate analogue, dehydroascorbate, and for sugar analogues such as alpha-D-glucose and 3-0-methyl-D-glucose (3-0-MG), but not for beta-D-fructose or L-glucose. Transport of ascorbate by cultured pericytes was insulin-insensitive. 3-0-Methyl-D-glucose inhibited ascorbate transport into pericytes in a non-competitive manner with a Ki of 22 mM. These results indicate that, in cultured retinal capillary pericytes, a common facilitated carrier diffusion system is involved in the transport of ascorbate and sugar analogues such as alpha-D-glucose or 3-0-MG.

Animals↗
PubMed1979

Decarboxylation and carboxylation of pyruvate in the living mice.

Mice received intravenously [1- or 2-14C]acetate, [1-, 2- or 3-14C] or [2-14C]pyruvate and were killed 1, 3, 5 or 15 min later. The radioactivity of CO2 or HCO3- of liver or carcass as well as the radioactivity of blood glucose were measured. The ratio of the radioactivity found in these compounds after [3-14C] or [2-14C-A1pyruvate injection suggests that in the fed aminals: 1. the decarboxylation of the pyruvate was more rapid than its carboxylation, 2. most of the neosynthesized glucose was derived from pyruvate molecules which had undergone a decarboxylation followed by a condensation to citrate, 3. 1/4 to 1/3 of the pyruvate was carboxylated and 2/3 to 3/4 was decarboxylated in animals receiving a diet poor in fats.

Acetates↗
PubMed1980

In vivo glucose turnover in hypo- and hyperthyroid starved rat.

The effect of hypo- and hyperthyroidism on glucose turnover in vivo was determined in unanesthetized rats starved for 48 h. Glucose pool and decay rate of specific radioactivity of blood glucose was measured after bolus injection of a mixture of 3H-(2)- and 14C-(U)-glucose under steady state conditions. Compared with euthyroid controls (= 100%), hypothyroidism resulted in a decrease of blood glucose concentration (81%), glucose pool (52%), glucose disappearance rate (39%), and total glucose recycling (12%). In contrast, hyperthyroidism led to an increase of blood glucose concentration (148%), glucose pool (121%), glucose disappearance rate (185%), and total glucose recycling (163%). T 1/2 for glucose was calculated to be 46 min in the hypo-, 34 min in the eu-, and 22 min in the hyperthyroid state. The concentration of circulating glucoregulatory hormones, corticosterone and glucagon were elevated in hyperthyroid rats, while glucagon was diminished in hypothyroid animals. No difference in the level of insulin was found. These data demonstrate that glucose turnover in vivo is a function of the thyroid state being reduced in hypo- and considerably increased in hyperthyroidism.

Animals↗
PubMed2003

Effect of fetal macrosomia on human placental glucose transport and utilization in insulin-treated gestational diabetes.

The aim of this study was to compare glucose transport and utilization in human placentae from pregnancies affected by insulin-treated GDM with and without macrosomia, and from non-diabetic control pregnancies. Placental lobules were perfused for 4 h. Maternal D-glucose concentration was 4, 8, 16, or 24 mM while the fetal D-glucose was maintained at 3mM. 14C-D-glucose and 3H-L-glucose were infused into the maternal circulation. Radioactivity, D-glucose and L-lactate levels were measured in the fetal and maternal effluent perfusates. Glucose uptake from the maternal perfusate, and transfer to the fetal effluent were not significantly different between groups. Insulin-treated GDM group without macrosomia had reduced glucose utilization compared to the control group while the insulin-treated GDM group with macrosomia did not. Lactate release into the fetal effluent was significantly reduced in both insulin-treated GDM groups compared to the control group. In conclusion, placental glucose utilization is different between insulin-treated GDM placentae with and without fetal macrosomia.

Adult↗
PubMed1972

Movement of C-Labeled Assimilates into Kernels of Zea mays L: I. Pattern and Rate of Sugar Movement.

Carbon-14, photosynthetically fixed in leaves of Zea mays L. and translocated to developing kernels, passed through specialized basal endosperm cells prior to movement into the starchy endosperm and embryo. Radioactivity migrated in the endosperm at a maximum rate of 2.7 millimeters per hour, and there was no difference in the rate of movement in kernels treated 14 to 30 days after pollination.Sucrose contained over three-fourths of the radioactivity in the kernal base (fruit stalk) 1 to 6 hours after (14)CO(2) treatment of the plant. Conversely, in the basal endosperm three-fourths of the radioactivity was in glucose and fructose. A high proportion of the radioactivity was retained in the monosaccharides of the starchy endosperm the first 3 hours after the (14)CO(2) treatment. With additional time after treatment there was a decline in the percentage of radioactivity in the monosaccharides and an increase in sucrose-(14)C. From these data we suggest that translocated sucrose is cleaved to glucose and fructose during entry into the endosperm and that the monosaccharides diffuse throughout the endosperm. Once the sugars arrive in the cells active in starch synthesis, they are rapidly converted to sucrose which in turn is utilized in the synthesis of starch.

Journal Article↗
PubMed1973

Lysis of Saccharomyces cerevisiae with 2-deoxy-2-fluoro-D-glucose, an inhibitor of the cell wall glucan synthesis.

The effect of a synthetic glucose analogue, 2-deoxy-2-fluoro-d-glucose (FG) on growth and glucose metabolism of Saccharomyces cerevisiae was studied. The addition of FG (0.005-0.05%) to a 2% glucose medium resulted in reduction of the initial growth rate and, after several hours, in a complete cessation of the culture growth. These two events were due to extensive lysis of the population which continued long after the period when no more growth was recorded. Electron microscope examination of lysed cells showed that the lysis was a consequence of a dissolution of the cell walls. FG inhibited to a similar extent the initial growth rate and the incorporation of radioactivity from labeled glucose into growing population. The inhibition of radioactivity incorporation from glucose by growing protoplasts was much less. The yeast was found to be extremely FG sensitive whenever the synthesis of new cell wall material was involved. All observations imply that FG interferes mainly with the cell wall formation of S. cerevisiae. A comparison of the FG effects on metabolic activity of protoplasts, simultaneous secretion of mannan-proteins into the growth medium, and the formation of glucan fibrils on the surface of protoplasts demonstrated that the cell wall glucan synthesis is the most FG-sensitive process and evidently the growth-limiting factor in intact cells. FG-resistant cells were selected during growth experiments. They exhibited an altered mode of cell division when grown in the presence of FG.

Autolysis↗
PubMed1969

Glucose uptake by isolated particles from rat epididymal tissue cells.

A MICROSOMAL FRACTION FROM ISOLATED ADIPOSE TISSUE CELLS HAS BEEN PREPARED WHICH POSSESSES MANY FEATURES INDICATING THE PRESENCE OF A FUNCTIONAL GLUCOSE TRANSPORT SYSTEM: (1) D-glucose is both taken up and released more rapidly than L-glucose at all temperatures, but at 42 degrees L-glucose uptake reaches the level of D-glucose after prolonged incubation; (2) D-glucose uptake is inhibited by a specific inhibitor of glucose transport, phlorizin, while L-glucose uptake is unaffected; (3) Preincubation of the preparation at 42 degrees C has no effect on L-glucose uptake but partially inhibits D-glucose uptake; (4) Equilibrium uptake studies show a linear relationship between the final level of D-glucose taken up and D-glucose concentration in the medium; and (5) Preloading the membrane preparation with unlabeled D-glucose leads to a more rapid uptake of radioactive D-glucose. These findings are interpreted as showing the presence in the microsomal particles of a specific, bidirectionally functioning D-glucose transport system superimposed on uptake of both sugars by passive diffusion or "leaks." The retained D-glucose can be eluted from the membrane preparation and shown to be the unphosphorylated sugar.

Adipose Tissue↗
PubMed1982

(1,3)-beta-D-Glucan synthase from budding and filamentous cultures of the dimorphic fungus Candida albicans.

UDPglucose:(1,3)-beta-D-glucan 3-beta-D-glucosyltransferase (EC 2.4.1.34) was obtained as a particulate fraction from cell-free extracts prepared after mechanical breakage of cells of a strain of the dimorphic fungus Candida albicans. The properties of this glucosyltransferase were investigated. Budding and filamentous cultures of C. albicans were grown after dilution of a stationary phase inoculum of yeast cells into fresh medium at 30 degrees C and 40 degrees C respectively and the specific activities of (1,3)-beta-D-glucan synthase, obtained from budding and filamentous cultures harvested during the first 3 h of their growth, were compared. 1. UDPglucose was the only glucosyl donor in the reaction (assayed by following the incorporation of radioactivity from UDP[14C]glucose into polymer) and the radioactive product was exclusively beta-(1,3)-glucan. 2. Glycogen synthase activity was not detected. 3. (1,3)-beta-D-Glucan synthase activity was enhanced by ATP and GTP. 4. A threefold increase in the specific activity of the glucosyltransferase was obtained when cell breakage, and subsequent steps in the preparation of the enzyme, were carried out in the presence of 25 microM GTP. A Km value for UDPglucose of 1.5-1.9 mM was obtained for the glucosyltransferase prepared in the presence or absence of GTP. 5. The glucosyltransferase reaction was not affected by ADPglucose, CDPglucose, GDPglucose or glucose 6-phosphate, but was competitively inhibited by TDPglucose. GDPglucose was not a glucosyl donor under the present conditions. 6. There was no evidence that the product was N-glycosidically linked to protein, since the reaction was neither enhanced in the presence of UDP-N-acetylglucosamine, nor inhibited by tunicamycin. 7. The specific activity of the glucosyltransferase from 3-h-old filamentous cultures was about 1.5-times higher than that from 3-h-old budding cultures. 8. The specific activities of (1,3)-beta-D-glucan synthase prepared from budding and filamentous cultures of C. albicans during their first 90 min of growth were similar.

Adenosine Triphosphate↗
PubMed1994

The addition of glucose-1-phosphate to the cytoplasmic glycoprotein phosphoglucomutase is modulated by intracellular calcium in PC12 cells and rat cortical synaptosomes.

In a number of different cell types, phosphorylation of a 63-kDa protein has been shown to increase rapidly in response to stimuli that lead to an increase in intracellular calcium. Here, a stimulus-sensitive protein at this molecular weight is identified in PC12 cells and rat cortical synaptosomes as phosphoglucomutase. In addition, the added phosphate is shown to be in an oligosaccharide terminating in phosphodiester-linked glucose. In synaptosomes, incorporated radioactivity, following incubation with [14C]glucose or the [beta-35S]phosphorothioate analogue of UDP-glucose, was found to increase within 5 s of stimulation and return to baseline within 25 s. Despite the many pathways utilizing glucose, this was the only detectable protein glycosylation observed in synaptosomes. These results indicate that cytoplasmic glycosylation is reversible and rapidly regulated, and suggest that phosphoglucomutase undergoes an alteration in function and/or topography in response to increases in intracellular calcium.

Animals↗
PubMed1994

A conformational model for the human liver microsomal glucose-6-phosphatase system: evidence from rapid kinetics and defects in glycogen storage disease type 1.

Rapid kinetics of glucose-6-phosphate (G6P) uptake and hydrolysis as well as of orthophosphate uptake were investigated in microsomes prepared from normal and glycogen storage disease type 1a (GSD 1a) human livers using a fast sampling, rapid filtration apparatus and were compared to those of rat liver microsomes. As shown before with rat microsomes, the production of [U-14C]glucose from 0.2 mmol/L [U-14C]G6P by untreated normal human microsomes was characterized by a burst in activity during the first seconds of incubation, followed by a slower linear rate. The initial velocity of the burst was equal to the rate of glucose production in detergent-treated microsomes. In untreated and detergent-treated GSD 1a microsomes, no glucose-6-phosphatase activity was observed. When untreated normal human or rat microsomes were incubated in the presence of 0.2 mmol/L [U-14C]G6P, an accumulation of [U-14C]glucose was observed, whereas no radioactive compound (G6P and/or glucose) was taken up by GSD 1a microsomes. Orthophosphate uptake was, however, detectable in both GSD 1a and normal untreated vesicles. These results do not support a rate-limiting transport of G6P in untreated normal human microsomes and further show that in this case of GSD 1a, no distinct G6P transport activity is present.

Adolescent↗
PubMed1985

Gluconeogenesis by the fetal sheep liver in vivo.

Hepatic gluconeogenesis is an important source of glucose postnatally. Whether hepatic gluconeogenesis contributes to fetal glucose supply has not been studied directly in vivo. Previous studies of gluconeogenesis in fetal sheep have assessed total fetal glucose production, and the results have been controversial. To assess the specific role of the liver in gluconeogenesis in fetal sheep, we placed catheters in the right or left hepatic vein, umbilical vein and the inferior vena cava of six fetal sheep (mean gestational age 134 days) and infused a radioactive gluconeogenic substrate (14C-lactate or 14C-alanine) into the fetal inferior vena cava. We measured 14C-glucose radioactivity (dpm/ml) in the right or left hepatic vein and calculated the arteriovenous difference in 14C-glucose radioactivity (dpm/ml) across the right or left liver lobe. We found that only 0.35% of the 14C substrates perfusing either the right or the left hepatic lobe of the fetal liver were converted to 14C-glucose. Even when considerable glucose was released by the liver, the percentage of substrates converted to glucose remained very low (maximum 1.7%), indicating that gluconeogenesis did not contribute significantly to the glucose released. We conclude that gluconeogenesis by the fetal liver contributes negligibly to the glucose supply in fetal sheep.

Alanine↗
PubMed1983

Influence of glucose on insulin handling by rat islets in culture. A reflection of integrated changes in insulin biosynthesis, release, and intracellular degradation.

Rat islets were maintained for 3 days in tissue culture at 2.8, 8.3, or 16.7 mM glucose, in the presence of [3H]leucine to label insulin stores. The immunoreactive insulin content of islets after 3 days at either 2.8 or 16.7 mM glucose was lower than that of islets exposed to 8.3 mM glucose. The specific radioactivity of stored labeled insulin, however, increased with increasing glucose. Islet insulin turnover was thus highest at 16.7 mM glucose. During a subsequent 1-day chase period at 2.8, 8.3, or 16.7 mM glucose for each of the three groups of islets prelabeled at these same three concentrations, all islets responded to glucose with increased insulin release. Release of immunoreactive insulin was highest at all three chase glucose concentrations for those islets preexposed for 3 days to 16.7 mM glucose. After 3-day labeling of islets at 8.3 mM glucose, there was an inverse relationship between the rate of release of labeled insulin and its intracellular degradation in response to the three glucose concentrations during the chase period. Those islets prelabeled at either 2.8 or 16.7 mM glucose showed much lower rates of intracellular degradation of labeled insulin stores during the chase period regardless of the ambient glucose or of the rate of release of the labeled hormone. Adaptive changes in islet insulin handling thus occurred during the 3-day maintenance period at different glucose concentrations. Whereas glucose concentration is, of course, thought to regulate insulin biosynthesis and release directly, regulation of degradation of stored insulin within B-cells appears to reflect both the relative activity of biosynthesis and release of the hormone and the insulin content of the islets. This last and striking relation is best interpreted as reflecting two labile, exchangeable, granule pools, one preferentially available for release and the other for intracellular degradation.

Animals↗
PubMed1981

Extensive radioactive labeling of glycolipids in cultured hamster fibroblasts by incubation of whole cells with UDP-[14C]glucose and UDP-[14C]galactose.

NIL 2cl cells, a cloned hamster cell line, are known to have seven classes of neutral glycosphingolipids in addition to hematoside. In this paper, I examined the participation of cell surface glycosyltransferases in the glycolipid synthesis in NIL cells. The cells, harvested from culture bottles by the use of chelating agents of divalent cations, incorporated radioactive glucose and galactose from labeled UDPglucose and UDPgalactose into endogenous glycolipid acceptors to form all eight classes of glycosphingolipids and dolichyl phosphate glucose. The major part of the incorporation occurred by glycosyltransferase reactions from nucleotide sugars, as indicated by a slight inhibition of the incorporation observed in the presence of a large excess of sugars or sugar phosphates. Acid hydrolysis of the glycolipid products showed that 91.4% of the 14C label was in the galactose and glucose moieties of the glycolipids. Exogenously added lactosylceramide stimulated the synthesis of trihexosylceramide in the absence of detergents. Th results presented in this paper suggest that incubation of whole cells with an equilibrium mixture of radioactive UDPglucose and UDPgalactose is a useful radioactive labeling method to determine the glycolipid composition of a cultured cell.

Animals↗