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PubMed1968

Effect of atractyloside on glucose and pyruvate metabolism in rat diaphragm muscle.

1. In the presence of 1.2mm-atractyloside oxygen uptake by rat diaphragm muscle incubated with 5.6mm-glucose decreases, as well as glycogen synthesis and carbon dioxide production. Lactate formation from glucose increases, but that of phosphoglycerate diminishes fivefold. 2. When pyruvate is used as substrate, atractyloside decreases oxygen uptake. 3. The specific radioactivity of the (14)CO(2) (mumoles of (14)CO(2)/mumole of oxygen), calculated at concentrations of [1-(14)C]pyruvate between 0.091mm and 91mm, lies between 3.1x10(-4) and 5.7x10(-1). Atractyloside increases the specific radioactivity of the (14)CO(2) with the lowest concentrations of substrate and has no effect when the substrate concentration is 91mm. 4. No appreciable effect of atractyloside on the anaerobic production of (14)CO(2) from [1-(14)C]pyruvate at various incubation times and various concentrations is found. 5. It is suggested that atractyloside induces anaerobic conditions in the tissue. Further, it produces a rise in the pyruvate concentration and an ATP deficiency in the cell. Consequently it stimulates pyruvate dismutation, and glycolysis, to which phosphorylation is linked at the substrate level.

Adenosine Triphosphate↗

PubMed1998

Simultaneous time-varying systemic appearance of oral and hepatic glucose in adults monitored with stable isotopes.

The rates (and extent) of appearance of glucose in arterialized plasma from an oral glucose load and from liver (RaO, RaH) can be estimated in humans using radioisotopes, but estimates vary among laboratories. We investigated the use of stable isotopes and undertook 22 primed intravenous infusions of D-[6,6-2H2]glucose with an oral load including D-[13C6]glucose in healthy humans. The effective glucose pool volume (VS) had a lower limit of 230 ml/kg body weight (cf. 130 ml/kg commonly assumed). This VS in Steele's one-compartment model of glucose kinetics gave a systemic appearance from a 50-g oral glucose load per 70 kg body weight of 96 +/- 3% of that ingested, which compared with a theoretical value of approximately 95%. Mari's two-compartment model gave 100 +/- 3%. The two models gave practically identical RaO and RaH at each point in time and a plateau in the cumulative RaO when absorption was complete. Less than 3% of 13C was recycled to [13C3]glucose, suggesting that recycling errors were practically negligible in this study. Causes of variation among laboratories are identified. We conclude that stable isotopes provide a reliable and safe alternative to radioactive isotopes in these studies.

Administration, Oral↗

PubMed1995

Autoradiographic analysis of the regional distribution of Glut3 glucose transporters in the rat brain.

Glut3 is a glucose transporter protein which facilitates the transport of glucose across the neuronal membranes. The local distribution of Glut3 in the brain is not well known. The present study had the aim to verify the local distribution of Glut3 in the brain and to compare it with the local glucose utilization. A polyclonal antibody directed against the C-terminal peptide sequence of Glut3 was applied to cryosections of rat brains. A secondary antibody was added which had been coupled to 35S. Using autoradiography and radioactive standards, 17 cerebral structures were investigated. The results show moderate differences of Glut3 density in the structures investigated ranging from -23% to +41% of the mean density. The pineal gland was an exception with a density 66% lower than mean. Local cerebral glucose utilization (LCGU) was analyzed in identical brain structures by application of the quantitative autoradiographic 2-deoxyglucose method to conscious rats. The range of LCGU was from -59% to +55% of the mean. No correlation was found between the moderately heterogeneous Glut3 transporter density and the strongly heterogeneous local cerebral glucose utilization. The results show that the local density of Glut3 glucose transporter protein does not reflect the local level of glucose utilization in the brain.

Animals↗

PubMed1976

Growth hormone and somatomedin A in girls with adolescent idiopathic scoliosis.

Girls with adolescent idiopathic scoliosis are taller than nonscoliotic girls of the same age. This observation may be related to factors regulating longitudinal growth. Plasma growth hormone was determined in a group of scoliotic girls by double antibody radioimmunoassay under the following conditions: 1) Insulin induced hypoglycemia, 2) glucose tolerance test, 3) exercise. Somatomedin A was determined by a method based on the ability of serum to stimulate the incorporation of radioactive sulphate in embryonic chick cartilage. The results were compared with those obtained in a control group of healthy nonscoliotic girls of comparable age. After overnight fasting and after at least one hour's rest the basal growth hormone level was 9.8+/-11.1 (+/-S.D.) ng/ml in the scoliotic girls (n=48) and 2.2+/-1.1 ng/ml in the controls (n=15). This difference is significant. In the hypoglycemia test the peak growth hormone level tended to be higher in the scoliotic girls but the difference is not significant. In the exercise test the maximal value was reached at different times in the two groups: at 20 min after start of the exercise in the scoliotic girls (n=14, 17.3+/-11.8 ng/ml) and at 40 min in the controls (n=9, 16.0+/-6.6 ng/ml). In the glucose tolerance test the growth hormone level was suppressed in both groups but the mean values tended to be higher during the first 120 min in the scoliotic girls. The serum somatomedin levels were higher in the group of scoliotic girls (n=19, 1.13+/-0.17 U/ml) than in the controls (n=14, 0.88+/-0.16 U/ml) and the difference is significant. The results obtained are difficult to interpret but suggest that growth hormone secretion is higher in girls with adolescent idiopathic scoliosis than in healthy girls of comparable age.

Adolescent↗

PubMed1985

Effect of tumour necrosis factor on growth of Ehrlich ascites tumour cells in vitro and in vivo.

Tumour necrosis factor (TNF) suppressed the growth of Ehrlich ascites tumour (EAT) cells in vitro and in vivo. Exposure of EAT cells to TNF for as little as 4 h totally abolished the transplantability of the tumour. At the same time, the rate of glucose uptake and extent of leucine incorporation were significantly reduced. Prolonged treatment with TNF resulted in extensive cell lysis, as determined by trypan blue exclusion and by release of radioactivity from [3H]thymidine-labelled EAT cells. The significance of these observations are discussed.

Animals↗

PubMed1991

Phosphoglucoisomerase-catalyzed interconversion of hexose phosphates. A model for D-[2-3H]glucose metabolism in human erythrocytes.

When D-[2-3H]glucose 6-phosphate mixed with the unlabeled ester is converted to D-[1-3H]fructose 6-phosphate and 3HOH in the phosphoglucoisomerase reaction and then to D-[1-3H]fructose 1,6-bisphosphate in the phosphofructokinase reaction, the specific radioactivity of the latter metabolite and the production of 3HOH relative to the total generation of tritiated end products are both inversely related to the concentration of phosphofructokinase. In human erythrocytes, the modeling of D-[2-3H]glucose metabolism, based on the activity of phosphoglucoisomerase in cell homogenates and on the steady-state content of D-glucose 6-phosphate and D-fructose 6-phosphate in intact cells, indicates that the back-and-forth interconversion of these esters is about five-times higher than the net glycolytic flux. Yet, the production of 3HOH from D-[2-3H]glucose is about 20% lower than the net glycolytic flux, as judged from the production of 3HOH from D-[5-3H]glucose. Thus, an incomplete detriation of D-[2-3H]glucose is not incompatible with an extensive interconversion of hexose 6-phosphates in the reaction catalyzed by phosphoglucoisomerase.

Animals↗

PubMed1983

Regional cerebral glucose utilization measured with [14C]glucose in brief experiments.

A method was developed to measure regional cerebral glucose utilization (rCMRGlc) in very short times using autoradiography and [2- 14C]glucose. It includes a more comprehensive mathematical treatment than prototypes and allows greater experimental flexibility. The current model takes into account the exchange of glucose between plasma and brain as a function of the plasma glucose concentration and rCMRGlc. The loss of 14C as 14CO2, although relatively small, is also calculated and the results corrected accordingly. Fully metabolizable radiolabeled glucose was chosen as the tracer, because it most closely resembles the natural substrate. Glucose is more rapidly phosphorylated than analogues such as 2-deoxyglucose and the 14C accumulated within intermediary metabolites soon account for most of the radioactivity in cerebral tissue. Furthermore, no special constant is necessary to adjust the rates as is the case when analogues are used. Excellent anatomic resolution was achieved when the technique was used to determine rCMRGlc in experiments as short as 5 min. By taking this approach, more short-lived phenomena may be studied under more diverse conditions than was previously possible.

Animals↗

PubMed1994

Synthesis and lymphatic transport of intestinal apolipoprotein A-IV in response to graded doses of triglyceride.

Factors regulating the intestinal synthesis and secretion of apoA-IV are incompletely understood. Although it is known that apoA-IV is stimulated by dietary lipid, it is not known whether graded doses of triglyceride elicit graded responses in apoA-IV synthesis and secretion. We used the chronic intestinal lymph-fistula rat to examine the effect of graded levels of intestinal triglyceride transport on secretion of apoA-IV into lymph and synthesis of apoA-IV in various regions of intestine. Rats were implanted with chronic duodenal and intestinal lymph duct cannulas and infused with lipid emulsions containing 5, 10, 20, 40, 80 mumol triolein (including [3H]triolein, 1.2 microCi), 8.7 mumol phosphatidylcholine, and 57 mumol sodium taurocholate in 3 ml phosphate-buffered saline (pH 6.4) at ml/h for 8 h. Lymph samples were collected for 1 h prior to and at 2, 4, 5, 6, 7, and 8 h after the start of lipid infusion. Lymphatic output of triglyceride, phospholipid, and apoA-IV was measured. Steady-state (8 h) content of radioactive lipid was also measured in the lumen and the wall of the gut. In separate studies rats were given infusions of either 5% glucose in saline ("fasting") or triolein emulsion (10, 20, 40, 80 mumol/h) for 8 h after which incorporation of [3H]leucine into apoA-IV in isolated, in situ loops of duodenum, proximal jejunum, mid-distal jejunum, and terminal ileum was measured. Lipid output increased dose-dependently in response to triolein infusion, with steady-state lipid transport achieved by 5 h after start of lipid infusion. Total recovery of 3H-labeled lipid was similar for all triolein doses. Increase in lymphatic apoA-IV output lagged that of triglyceride by 3-4 h, but by 8 h showed graded increases with triolein dose. ApoA-IV synthesis (apoA-IV radioactivity immunoprecipitated by an apoA-IV monospecific antibody and expressed as % of trichloroacetic acid-precipitable [3H]leucine radioactivity) in the duodenum and proximal jejunum showed a 2-fold increase (compared with fasting) in response to 10 mumol triolein/h, but no further increase at higher doses. However, apoA-IV synthesis in mid to distal jejunum increased dose-dependently.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1990

Intramuscular versus subcutaneous injection of unmodified insulin: consequences for blood glucose control in patients with type 1 diabetes mellitus.

Using the perpendicular injection technique lean diabetic patients may often inject insulin intramuscularly (IM). Guided by ultrasound measurements of the subcutaneous (SC) thickness of the thigh, the aim of the present study was to re-evaluate the absorption kinetics of unmodified insulin from IM and SC injection sites and to evaluate the consequences of IM injection of unmodified insulin for blood glucose control in Type 1 diabetic patients. T50% values (time until 50% of the injected insulin is absorbed from the injection site) of SC injected, radioactively labelled, human unmodified insulin (125I-Actrapid) were 338 +/- 13 (+/- SE) min, 289 +/- 27 min, and 287 +/- 27 min during rest, light physical activity, and strenuous exercise, respectively. Intramuscularly injected unmodified insulin was absorbed faster, T50% 232 +/- 20 min, 113 +/- 13 min, and 112 +/- 5 min during the same levels of physical activity in the same order. When unmodified insulin (Actrapid) was given IM 30 min before breakfast, lunch, and dinner together with intermediate-acting insulin (Protaphane) SC at 2200 h, a more physiological profile of plasma free insulin and a more stable blood glucose profile was obtained than with SC administration into the thigh. The coefficient of variation of blood glucose concentration during the study (3 days each route) was lower with IM than with SC injection of unmodified insulin (33 +/- 4 vs 43 +/- 3%, p less than 0.01). No difference in frequency of hypoglycaemic attacks was found and patients claimed that IM injection was no more painful than SC injection. These data suggest that IM injection of soluble insulin into the thigh is beneficial.

Adipose Tissue↗

PubMed1982

Trehalase: stereocomplementary hydrolytic and glucosyl transfer reactions with alpha- and beta-D-glucosyl fluoride.

A new understanding has been obtained of the catalytic capabilities of trehalase, an enzyme heretofore held to be strictly specific for hydrolyzing alpha, alpha-trehalose and devoid of transglycosylative ability. Highly purified rabbit renal cortical trehalase and a partly purified Candida tropicalis yeast trehalase were found to utilize both alpha- and beta-D-glucosyl fluoride as substrates. In each case, the reactions were competitively inhibited by alpha, alpha-trehalose. Both enzymes catalyzed rapid hydrolysis of alpha-D-glucosyl fluoride to form beta-D-glucose (also, of alpha, alpha-trehalose to form equimolar alpha- and beta-D-glucose). In addition, digests of beta-D-glucosyl fluoride plus alpha-D-[14C]-glucopyranose with either trehalase (but not controls of enzyme with alpha-D-[14C]glucopyranose alone) yielded small amounts of radioactive trehalose (alpha-D-glucopyranosyl alpha-D-[14C]glucopyranoside) which does not accumulate since it is rapidly hydrolyzed. Trehalase thus catalyzes two stereocomplementary types of glycosylation reactions: (I) alpha-D-glucosyl fluoride (or alpha, alpha-trehalose) + H2O leads to beta-D-glucose + HF (or alpha-D-glucose); (II) beta-D-glucosyl fluoride + alpha-D-glucopyranose leads to alpha, alpha-trehalose + HF. Such behavior shows that the catalytic groups of trehalase, as recently found for other glycosylases, are functionally flexible. The results illustrate the inadequacy of conventional views of carbohydrase specificity and the rigor, as a basic guiding principle, of the concept that glycoside hydrolases and glycosyltransferases form a class of glycosylases effecting glycosyl/proton interchange.

Animals↗

PubMed1973

Effects of dichloroacetate on the metabolism of glucose, pyruvate, acetate, 3-hydroxybutyrate and palmitate in rat diaphragm and heart muscle in vitro and on extraction of glucose, lactate, pyruvate and free fatty acids by dog heart in vivo.

1. The extractions of glucose, lactate, pyruvate and free fatty acids by dog heart in vivo were calculated from measurements of their arterial and coronary sinus blood concentration. Elevation of plasma free fatty acid concentrations by infusion of intralipid and heparin resulted in increased extraction of free fatty acids and diminished extractions of glucose, lactate and pyruvate by the heart. It is suggested that metabolism of free fatty acids by the heart in vivo, as in vitro, may impair utilization of these substrates. These effects of elevated plasma free fatty acid concentrations on extractions by the heart in vivo were reversed by injection of dichloroacetate, which also improved extraction of lactate and pyruvate by the heart in vivo in alloxan diabetes. 2. Sodium dichloroacetate increased glucose oxidation and pyruvate oxidation in hearts from fed normal or alloxan-diabetic rats perfused with glucose and insulin. Dichloroacetate inhibited oxidation of acetate and 3-hydroxybutyrate and partially reversed inhibitory effects of these substrates on the oxidation of glucose. In rat diaphragm muscle dichloroacetate inhibited oxidation of acetate, 3-hydroxybutyrate and palmitate and increased glucose oxidation and pyruvate oxidation in diaphragms from alloxan-diabetic rats. Dichloroacetate increased the rate of glycolysis in hearts perfused with glucose, insulin and acetate and evidence is given that this results from a lowering of the citrate concentration within the cell, with a consequent activation of phosphofructokinase. 3. In hearts from normal rats perfused with glucose and insulin, dichloroacetate increased cell concentrations of acetyl-CoA, acetylcarnitine and glutamate and lowered those of aspartate and malate. In perfusions with glucose, insulin and acetate, dichloroacetate lowered the cell citrate concentration without lowering the acetyl-CoA or acetylcarnitine concentrations. Measurements of specific radioactivities of acetyl-CoA, acetylcarnitine and citrate in perfusions with [1-(14)C]acetate indicated that dichloroacetate lowered the specific radio-activity of these substrates in the perfused heart. Evidence is given that dichloroacetate may not be metabolized by the heart to dichloroacetyl-CoA or dichloroacetylcarnitine or citrate or CO(2). 4. We suggest that dichloroacetate may activate pyruvate dehydrogenase, thus increasing the oxidation of pyruvate to acetyl-CoA and acetylcarnitine and the conversion of acetyl-CoA into glutamate, with consumption of aspartate and malate. Possible mechanisms for the changes in cell citrate concentration and for inhibitory effects of dichloroacetate on the oxidation of acetate, 3-hydroxybutyrate and palmitate are discussed.

Acetates↗

PubMed1990

PET studies of dopamine receptor distribution using [18F]fluoroethylspiperone: findings in disorders related to the dopaminergic system.

PET studies of dopamine D2-receptor binding were performed in thirty patients with various disorders related to the dopaminergic system and in six healthy controls. Uptake of [18F]fluoroethylspiperone in caudate over three hours was analyzed in terms of several indices of receptor binding:caudate-to-cerebellum activity ratio, concentration of ligand as percentage of injected dose, caudate-to-blood radioactivity ratio, slope of tracer uptake curves, binding potential, kinetic constants of a three compartment model. In 14 patients brain glucose metabolism was also measured. Data on medicated patients demonstrate that the average values of most of the above parameters indicate the decreased number of available D2-receptors whereby, besides an age dependent decline, the caudate-to-cerebellum ratio affords the relatively best distinction among diagnostic groups. In individual cases, large variability among subjects permits only the classification of severe pathologies. Morphological damage and neuronal loss in the striatum may also cause abnormal low values both for the indices of receptor binding and for glucose consumption, thus providing a possible pathogenetic link between receptor dysfunction and impaired energy metabolism.

Adolescent↗

PubMed1994

Cerebral effects of low-flow cardiopulmonary bypass and hypothermic circulatory arrest.

Although both hypothermic circulatory arrest (HCA) and low-flow cardiopulmonary bypass (CPB) are accepted techniques for the operative management of complex cardiovascular pathology, the potential for neurologic sequelae is still a concern. To assess the relative safety of these techniques, we compared cerebral hemodynamics and clinical outcome in two groups of puppies. Sixteen puppies underwent 45 minutes of either HCA or low-flow CPB (25 mL.kg-1.min-1) after cooling to 13 degrees C. Methodology included radioactive microsphere determination of cerebral blood flow; calculation of cerebral oxygen extraction (arteriovenous oxygen content difference) and consumption; measurement of glucose consumption, and determination of cerebrovascular resistance. Measurements were obtained at baseline (37 degrees C), 13 degrees C, and 30 degrees C and at 2, 4, and 8 hours after HCA or low-flow CPB. No neurologic deficits were observed in any of the survivors (15/16). In both groups, cerebral metabolic rate of oxygen was maintained at baseline or greater levels postoperatively. Cerebrovascular resistance rose slightly in the low-flow CPB group postoperatively in contrast to a marked elevation in the HCA group. During the period of high cerebrovascular resistance after HCA, cerebral metabolic rate of oxygen was maintained by increased oxygen extraction. After low-flow CPB, oxygen extraction was not significantly different from baseline, presumably because of less severe changes in cerebrovascular resistance. Glucose metabolism followed the same trends as oxygen metabolism in both groups. These data suggest that after HCA there is a vulnerable interval, lasting as late as 8 hours postoperatively, in which cerebrovascular resistance remains high and cerebral metabolism is maintained primarily by high oxygen and glucose extraction. Any additional stress during this interval (a decrease in arterial oxygen content or perfusion pressure) could result in cerebral injury.

Animals↗

PubMedDate not supplied

A positron-emitting internal marker for identification of normal tissue by positron emission tomography: phantom studies and validation in patients.

PURPOSE: This study evaluated in a phantom model and verified in patients with lung cancer whether the use of an internal positron-emitting labeled marker could localize a critical structure by positron emission tomography (PET) imaging and verify multimodality image registration. MATERIALS AND METHODS: An initial device and method were developed to demonstrate by dedicated PET the location of the normal esophagus in a phantom and in three patients using a column of 2-deoxy-2-[18F]fluoro-D-glucose (FDG) solution between proximal and distal gas phases in polyurethane tubing. The device was assessed for possible loss of radioactivity. PET, CT and PET-CT fusion imaging followed. RESULTS: X-rays of the marker device showed a continuous fluid column. No leakage of contents was detected. The internal marker in the phantom and in patients allowed visualization by PET of the esophagus, and verified an image registration algorithm. CONCLUSIONS: A positron-emitting internal marker was constructed, demonstrated to retain tracer, and shown to be capable of verifying an image registration algorithm and identifying a critical structure, the esophagus, by PET in a phantom and in patients.

Carcinoma, Non-Small-Cell Lung↗

PubMed2000

Novel processive and nonprocessive glycosyltransferases from Staphylococcus aureus and Arabidopsis thaliana synthesize glycoglycerolipids, glycophospholipids, glycosphingolipids and glycosylsterols.

A processive diacylglycerol glucosyltransferase has recently been identified from Bacillus subtilis [Jorasch, P., Wolter, F.P., Zähringer, U., and Heinz, E. (1998) Mol. Microbiol. 29, 419-430]. Now we report the cloning and characterization of two other genes coding for diacylglycerol glycosyltransferases from Staphylococcus aureus and Arabidopsis thaliana; only the S. aureus enzyme shows processivity similar to the B. subtilis enzyme. Both glycosyltransferases characterized in this work show unexpected acceptor specificities. We describe the isolation of the ugt106B1 gene (GenBank accession number Y14370) from the genomic DNA of S. aureus and the ugt81A1 cDNA (GenBank accession number AL031004) from A. thaliana by PCR. After cloning and expression of S. aureus Ugt106B1 in Escherichia coli, SDS/PAGE of total cell extracts showed strong expression of a protein having the predicted size of 44 kDa. Thin-layer chromatographic analysis of the lipids extracted from the transformed E. coli cells revealed several new glycolipids and phosphoglycolipids not present in the controls. These lipids were purified from lipid extracts of E. coli cells expressing the S. aureus gene and identified by NMR and mass spectrometry as 1, 2-diacyl-3-[O-beta-D-glucopyranosyl]-sn-glycerol, 1, 2-diacyl-3-[O-beta-D-glucopyranosyl-(1-->6)-O-beta-D-glucopyrano-+ ++syl] -sn-glycerol, 1, 2-diacyl-3-[O-beta-D-glucopyranosyl-(1-->6)-O-beta-D-glucopyranosyl-( 1-->6)-O-beta-D-glucopyranosyl]-sn-glycerol, sn-3'-[O-beta-D-glucopyranosyl]-phosphatidylglycerol and sn-3'-[O-(6"'-O-acyl)-beta-D-glucopyranosyl-(1"'-->6")-O-beta-D-gluco pyranosyl]-sn-2'-acyl-phospha-tidylglycerol. A 1, 2-diacyl-3-[O-beta-D-galactopyranosyl]-sn-glycerol was isolated from extracts of E. coli cells expressing the ugt81A1 cDNA from A. thaliana. The enzymatic activities expected to catalyze the synthesis of these compounds were confirmed by in vitro assays with radioactive substrates. Experiments with several of the above described glycolipids as 14C-labeled sugar acceptors and unlabeled UDP-glucose as glucose donor, suggest that the ugt106B1 gene codes for a processive UDP-glucose:1, 2-diacylglycerol-3-beta-D-glucosyltransferase, whereas ugt81A1 codes for a nonprocessive diacylglycerol galactosyltransferase. As shown in additional assays with different lipophilic acceptors, both enzymes use diacylglycerol and ceramide, but Ugt106B1 also accepts glucosyl ceramide as well as cholesterol and cholesterol glucoside as sugar acceptors.

Amino Acid Sequence↗

PubMed1975

Chitin synthetase zymogen is attached to the yeast plasma membrane.

Pretreatment of yeast protoplasts with concanavalin A, according to the method used by G. A. Scarborough for Neurospora (J. Biol. Chem. 250, 1106-1111, 1975), reinforced the plasma membranes, and helped to maintain their integrity during subsequent lysis of the protoplasts. After purification by centrifuging on a Renografin density gradient, practically intact membranes were obtained. Previous labeling of the protoplasts with 125I or with [3H]concanavalin A resulted in recovery of the radioactivity in the membrane fraction. The bulk of the chitin synthetase (chitin synthase; UDP-2-acetamido-2-deoxy-D-glucose:chitin 4-beta-acetamidodeoxyglucosyltransferase; EC 2.4.1.16) recovered in the gradient was also found In this fraction; in the zymogen form. About 20% of the activity sedimented in a plasma-membrane-free fraction at lower density. Glutaraldehyde inactivated chitin synthetase when it was added to a lysate, but not when applied to intact protoplasts. It is concluded that chitin synthetase is so oriented in the membrane that it is only accessible from the inside of the cell. These results confirm our previous hypothesis that the chitin synthetase zymogen is associated with the plasma membrane, a basic assumption for the explanation of localized activation of the enzyme and initiation of septum formation.

Cell Fractionation↗

PubMed1992

Differential diagnosis of idiopathic fibrosis from malignant lymphadenopathy with PET and F-18 fluorodeoxyglucose.

Idiopathic fibrosis and malignant lymphoma were studied with positron emission tomography (PET) using 2-deoxy-2-[F-18]fluoro-D-glucose (F-18DG). Cases of retroperitoneal fibrosis and sclerosing peritonitis showed low F-18DG uptake with the mass/muscle radioactivity (M/M) ratio 2.0 and 1.9, respectively. A case of para-aortic adenopathy from malignant lymphoma showed high F-18DG uptake with the M/M ratio 9.4. F-18DG PET study may be useful for the differential diagnosis of idiopathic fibrosis and malignant lymphadenopathy.

Aged↗

PubMed1992

Assessment of glucose turnover rates in euglycaemic clamp studies using primed-constant [3-3H]-glucose infusion and labelled or unlabelled glucose infusates.

Underestimation of glucose turnover rates has been a problem in clamp studies using primed-constant [3-3H]-glucose infusion technique. Due to slow mixing in interstitial compartments concealed specific activity gradients may arise between plasma and interstitial compartments during intravenous unlabelled glucose infusion. Such specific activity gradients, however, can be prevented if plasma specific activity is maintained constant. Two euglycaemic clamp studies (insulin infusion 40 mU m-2 min-1) were performed in six lean normal subjects. Using conventional unlabelled glucose infusates plasma specific activity declined by 74%, tracer determined glucose appearance was smaller than actual glucose infusion rates (317 +/- 11 vs 366 +/- 15 mg m-2 min-1, p < 0.001), and erroneous negative values were calculated for glucose production (- 49 +/- 7 mg m-2 min-1). Average underestimation during the first 2 h correlated with glucose infusion rates (r = 0.88, p < 0.02). In contrast, when plasma specific activity was maintained constant, using appropriately labelled glucose infusates, tracer determined glucose appearance and glucose infusion rates were similar (385 +/- 16 vs 385 +/- 17 mg m-2 min-1), and negative errors for glucose production were avoided. In conclusion, using unlabelled glucose infusates, as in previous studies, suppression of glucose production is overestimated and stimulation of glucose utilization is underestimated. As errors were greater with larger glucose infusions, the mistakes may have been greatest in insulin sensitive control subjects, and smaller in insulin resistant subjects. Therefore, re-evaluation of hepatic insulin sensitivity seems appropriate in diabetes, obesity, and other insulin resistant states.

Adult↗