Diagnosis of bone metastasis by thermography

The uptake of D-[(14)C]mannose by adult rat kidney cortex slices has been examined. The process involved appeared to be saturable and oxygen dependent and to be inhibited by glucose, galactose, chi-methyl-D-glucoside, and phlorizin. Extensive metabolism of the sugar occurred. (14)CO(2) was produced to an extent comparable to that from D-glucose. Radioactive compounds accumulated in the tissue, approximately 50% of which were in the form of phosphorylated or other polar intermediates. The remaining neutral fraction consisted of mannose with a small amount of label in glucose and an unidentified compound which behaves like an alditol. Mannose concentration in the intracellular fluid was never greater than that of the medium.     

Fasting does not impair insulin-stimulated glucose uptake but alters intracellular glucose metabolism in conscious rats

Effects of 24-h and 48-h fasting on maximal insulin-stimulated whole-body and muscle glucose uptake, glycogen synthesis, and glycolysis were studied in conscious rats by combining the glucose clamp technique with tracer methods. Fasting decreased body weight and basal plasma glucose, plasma insulin, hepatic glucose output, and glucose clearance (P < 0.05 for all). However, maximal insulin-stimulated whole-body glucose uptake, normalized to body weight, was almost identical in fed, 24-h fasted, and 48-h fasted rats (191 +/- 8, 185 +/- 14, and 182 +/- 5 mumol.kg-1.min-1, respectively; P > 0.7). Similarly, rates of insulin-stimulated glucose uptake by four different skeletal muscles, estimated by the 2-deoxyglucose injection technique, were not different among the three groups. In contrast to glucose uptake, insulin-stimulated whole-body glycolysis was decreased significantly after fasting (36% after 48 h fasting; P < 0.05), whereas insulin-stimulated whole-body glycogen synthesis was increased (44% after 48 h fasting; P < 0.05). In fed rats, glycolysis was the major pathway for glucose metabolism during hyperinsulinemia, accounting for 60 +/- 5% of glucose uptake. This fraction was decreased significantly by fasting (P < 0.01), so that after a 48-h fast, glycolysis accounted for only 40 +/- 3% of insulin-stimulated glucose uptake and glycogen synthesis became predominant pathway, accounting for 60 +/- 3% of whole-body glucose utilization. Whole-body patterns of glucose metabolism during hyperinsulinemia were paralleled by glucose metabolism in individual muscles.(ABSTRACT TRUNCATED AT 250 WORDS)     

Calcium channel blockers modify jejunal uptake of D-galactose in rabbits

Calcium channel blockers modify the intestinal uptake of lipids. This study was undertaken to test the hypothesis that two different types of calcium channel blockers influence the uptake of D-galactose, a sugar absorbed by the sodium-dependent glucose transporter (SGLT1) in the intestinal brush border membrane. Nisoldipine (1 mg/kg/day) or verapamil (4 mg/kg/day) were given by mouth to New Zealand white rabbits for three weeks, and then the rates of uptake of varying concentrations (2-64 mM) of galactose were examined in an in vitro preparation of jejunum using the incorporation of 14C-labeled substrate into intact tissue segments. The maximal transport capacities (Vmax) for D-galactose were increased in animals given nisoldipine or verapamil, as compared to controls. The value of the apparent Michaelis constant Km* for D-galactose was higher with nisoldipine group and lower with verapamil, than in controls. The apparent passive permeability (Pd*) of D-galactose was estimated from the uptake of L-glucose: Pd* was lower with nisoldipine and higher with verapamil, as compared to controls. The effect of these drugs on sugar uptake is not due to differences in the animals' food intake, body weight gain, or mucosal surface area. Thus, the two different classes of calcium channel blockers, the dihydropyridine nisoldipine and the phenylalkylamine verapamil, have different effects on the K(m)* and Pd*, but not on the Vmax of D-galactose uptake.     

Oxidation of exogenous [13C]galactose and [13C]glucose during exercise

The present study examined the oxidation of exogenous galactose or glucose during prolonged submaximal cycling exercise. Eight highly trained volunteers exercised on two occasions on a cycle ergometer at 65% of maximal workload for 120 min, followed by a 60-min rest period and a second exercise bout of 30 min at 60% maximal workload. At random, subjects ingested a 8% galactose solution to which an [1-13C]galactose tracer was added or a 8% glucose solution to which an [U-13C]glucose tracer was added. Drinks were provided at the end of the warm-up period (8 ml/kg) and every 15 min (2 ml/kg) during the first 120 min of the test. Blood and breath samples were collected every 30 and 15 min, respectively, during the test. The exogenous carbohydrate (CHO) oxidation was calculated from the 13CO2/12CO2 ratio and CO2 production of the expired air. Peak exogenous CHO oxidation during exercise for galactose and glucose was 0.41 +/- 0.03 and 0.85 +/- 0.04 g/min, respectively. Total CHO and fat oxidation were not significantly different between the treatments. Forty-six percent of the ingested glucose was oxidized, whereas only 21% of the ingested galactose was oxidized. As a consequence, more endogenous CHO was utilized with galactose than with glucose (124.4 +/- 6.7 and 100.1 +/- 3.6 g, respectively). These results indicate that the oxidation rate of orally ingested galactose is maximally approximately 50% of the oxidation rate of a comparable amount of orally ingested glucose during 120 min of exercise.     

Myocardial glucose uptake and breakdown during adenosine-induced vasodilation

In isolated K+ (16.2 mM)-arrested cat hearts perfused at constant pressure adenosine infusions (0.8 mumoles - min-1 - 100 g-1 for 10 min) caused an increase in myocardial 14C-glucose uptake and release of 14CO2 + H14CO3- AND 14C-lactate simultaneously with a rise in coronary flow. The ratio of the release of 14CO2 + H14CO3- to that of 14C-lactate and the specific activity of lactate in the effuate were not altered. In K+ -arrested hearts perfused with constant volume neither glucose uptake nor glucose breakdown were influenced by 0.8 or 100 mumoles - min-1 - 100 g-1 adenosine with 0.1 - 5 mM glucose in the perfusion medium. It is concluded that adenosine does not affect directly the myocardial glucose carrier system, aerobic or anaerobic glucose breakdown or glycogenolysis, but enhances glucose uptake secondarily by increasing coronary flow. This interpretation is substantiated by the finding that mechanically produced increases in perfusion volume caused similar increases in myocardial glucose uptake as were observed with comparable adenosine-induced coronary flow increments.     

Estimates of glycolysis, pyruvate (de)carboxylation, pentose phosphate pathway, and methyl succinate metabolism in incapacitated pancreatic islets

Pancreatic islets were cultured for 24 h in the presence of 1 mM glucose, which renders islets incapable of responding to glucose with insulin release. These islets were compared to islets maintained at 20 mM glucose for 24 h. Detritiation of [2-3H]glucose and [5-3H]glucose in 1 mM glucose islets was normal, suggesting that glucose transport and phosphorylation and all enzymes of glycolysis were not down-regulated in the incapacitated islets. 14CO2 formation from [U-14C]glucose and [6-14C]glucose was inhibited up to 80% and 14CO2 from methyl succinate was inhibited up to 60%, indicating that down-regulation at (a) mitochondrial site(s) might explain the incapacitated insulin release. 14CO2 formation from [3,4-14C]glucose (which becomes [1-14C]pyruvate) was decreased, indicating that the reaction catalyzed by pyruvate dehydrogenase was down-regulated. This decrease, however, was not as large as the decreases in 14CO2 formation from [U-14C]glucose, [2-14C]glucose (which becomes [2-14C]pyruvate), or [6-14C]glucose (which becomes [3-14C]pyruvate), indicating that other reactions were also down-regulated. 14CO2 formation from [1-14C]glucose was inhibited less than that from [6-14C]glucose in the incapacitated islets (34 vs 54%) and these rates indicated that flux of glucose through the pentose phosphate pathway was increased in the incapacitated islet, such that 29% (0.4 nmol of 1.4 glucose/100 islets/90 min) was metabolized via this pathway in the incapacitated islet but only 3.4% (0.1 of 2.9 nmol glucose/100 islets/90 min) was metabolized via the pentose pathway in the 20 mM glucose islets. With rates of 14CO2 evolved from glucose labeled at C2 and C6 and from methyl succinate labeled at C1 + C4 and C2 + C3 the 14CO2 ratio formula was used to calculate the ratios of carboxylated and decarboxylated pyruvate. Roughly equal amounts of pyruvate entered the citric acid cycle by each route in islets maintained for 24 h at 1, 5, or 20 mM glucose. The results indicate that decarboxylation and carboxylation of pyruvate were about equally suppressed in incapacitated islets and that direct inhibition of reactions of the cycle was unlikely. This is consistent with evidence which indicates that down-regulation of both pyruvate carboxylase and pyruvate dehydrogenase occurs in incapacitated islets, i.e., under long-term conditions that modify amounts of enzymes (MacDonald et al., 1991, J. Biol. Chem. 266, 22392-22397).(ABSTRACT TRUNCATED AT 400 WORDS)     

Effects of fatty acid oxidation on glucose utilization by isolated hepatocytes

We have studied the inhibitory action of long- and short-chain fatty acids on hepatic glucose utilization in hepatocytes isolated from fasted rats. The rates of hepatic glucose phosphorylation and glycolysis were determined from the tritiated products of [2-3H] and [6-3H]glucose metabolism, respectively. The difference between these was taken as an estimate of the 'cycling' between glucose and glucose-6-phosphate. In the presence of 40 mM glucose this cycling was estimated at 0.68 mumol/min/g wet wt. Glucose phosphorylation was unaffected during palmitate and hexanoate oxidation to ketone bodies but glycolysis was inhibited. The rate of glucose cycling was increased during this phase to 1.25 mumol/min/g. Following the complete metabolism of the fatty acids, glycolysis was reinstated and cycling rates returned to control levels. Hepatic glucose cycling appears to be an important component of the glucose/fatty acid cycle.     

Lactate is released and taken up by isolated rabbit vagus nerve during aerobic metabolism

To determine if lactate is produced during aerobic metabolism in peripheral nerve, we incubated pieces of rabbit vagus nerve in oxygenated solution containing D-[U-14C]glucose while stimulating electrically. After 30 min, nearly all the radioactivity in metabolites in the nerve was in lactate, glucose 6-phosphate, glutamate, and aspartate. Much lactate was released to the bath: 8.2 pmol (microg dry wt)(-1) from the exogenous glucose and 14.2 pmol (microg dry wt)(-1) from endogenous substrates. Lactate release was not increased when bath PO2 was decreased, indicating that it did not come from anoxic tissue. When the bath contained [U-14C]lactate at a total concentration of 2.13 mM and 1 mM glucose, 14C was incorporated in CO2 and glutamate. The initial rate of formation of CO2 from bath lactate was more rapid than its formation from bath glucose. The results are most readily explained by the hypothesis that has been proposed for brain tissue in which glial cells supply lactate to neurons.     

Characterization of cellular defects of insulin action in type 2 (non-insulin-dependent) diabetes mellitus

Seven non-insulin-dependent diabetes mellitus (NIDDM) patients participated in three clamp studies performed with [3-3H]- and [U-14C]glucose and indirect calorimetry: study I, euglycemic (5.2 +/- 0.1 mM) insulin (269 +/- 39 pM) clamp; study II, hyperglycemic (14.9 +/- 1.2 mM) insulin (259 +/- 19 pM) clamp; study III, euglycemic (5.5 +/- 0.3 mM) hyperinsulinemic (1650 +/- 529 pM) clamp. Seven control subjects received a euglycemic (5.1 +/- 0.2 mM) insulin (258 +/- 24 pM) clamp. Glycolysis and glucose oxidation were quantitated from the rate of appearance of 3H2O and 14CO2; glycogen synthesis was calculated as the difference between body glucose disposal and glycolysis. In study I, glucose uptake was decreased by 54% in NIDDM vs. controls. Glycolysis, glycogen synthesis, and glucose oxidation were reduced in NIDDM patients (P < 0.05-0.001). Nonoxidative glycolysis and lipid oxidation were higher. In studies II and III, glucose uptake in NIDDM was equal to controls (40.7 +/- 2.1 and 40.7 +/- 1.7 mumol/min.kg fat-free mass, respectively). In study II, glycolysis, but not glucose oxidation, was normal (P < 0.01 vs. controls). Nonoxidative glycolysis remained higher (P < 0.05). Glycogen deposition increased (P < 0.05 vs. study I), and lipid oxidation remained higher (P < 0.01). In study III, hyperinsulinemia normalized glycogen formation, glycolysis, and lipid oxidation but did not normalize the elevated nonoxidative glycolysis or the decreased glucose oxidation. Lipid oxidation and glycolysis (r = -0.65; P < 0.01), and glucose oxidation (r = -0.75; P < 0.01) were inversely correlated. In conclusion, in NIDDM: (a) insulin resistance involves glycolysis, glycogen synthesis, and glucose oxidation; (b) hyperglycemia and hyperinsulinemia can normalize total body glucose uptake; (c) marked hyperinsulinemia normalizes glycogen synthesis and total flux through glycolysis, but does not restore a normal distribution between oxidation and nonoxidative glycolysis; (d) hyperglycemia cannot overcome the defects in glucose oxidation and nonoxidative glycolysis; (e) lipid oxidation is elevated and is suppressed only with hyperinsulinemia.     

Effects of rho-chloroamphetamine on locomotor activity and brain 5-hydroxyindoles

The conversion of 14C-maltose into glucose, lactate and 14 CO2 was studied in perfused livers from fed and fasted rats and in isolated hepatocytes. Maximal glucose production was 30 mM x g-1 x h-1; half-maximal rates were found with 3 mM maltose. About 0.01 % of the radioactivity infused was recovered as 14CO2. The addition of maltose had no effect on rates of oxygen consumption, lactate production or ketogenesis. The data suggest that maltose did not serve as a major substrate for biosynthetic or energy producing processes under the conditions of the perfused rat liver.     

Decreased basal, noninsulin-stimulated glucose uptake and metabolism by skeletal soleus muscle isolated from obese-hyperglycemic (ob/ob) mice

Insulin resistance of diaphragms of ob/ob mice has been repeatedly demonstrated previously both in vitro and in vivo. In the present study, transport and metabolism of glucose with and without insulin stimulation were compared in a skeletal muscle more likely than diaphragm or heart to be representative of the overall striated muscle mass, i.e. isolated soleus muscle. Compared with soleus muscle from lean controls, unstimulated lactate release in the presence of exogenous glucose was depressed from 16.2 to 12.3 nmol/60 min per mg wet wt in soleus from ob/ob mutants; glycolysis was decreased from 6.6 to 3.7 and [14C]glucose oxidation to 14CO2 from 0.90 to 0.33 nmol glucose/60 min per mg wet wt. Uptake of 2-deoxyglucose (2-DOG), both with and without insulin, was very much less for soleus from ob/ob than from lean mice, at 2-DOG concentrations ranging from 0.1 to 10 mM, and in mice of 6-15 wk. When 2-DOG concentration was 1 mM, its basal uptake was 0.53 nmol/30 min per mg wet wt for soleus of ob/ob as against 0.96 for soleus of lean mice. The absolute increment due to 1 mU/ml insulin was 0.49 in muscle of ob/ob as against 1.21 in that of lean mice. When the resistance to insulin action was decreased by pretreatment in vivo by either streptozotocin injection or fasting, the decreased basal 2-DOG uptake of subsequently isolated soleus muscle was not improved. Inhibition of endogenous oxidation of fatty acids by 2-bromostearate, while greatly increasing 14CO2 production from [14C]glucose, did not affect basal [5-3H]glucose metabolism or 2-DOG uptake. It is suggested that transport and/or phosphorylation of glucose under basal, unstimulated conditions are depressed in soleus muscle of ob/ob mice, whether or not resistance to insulin and hyperinsulinemia are also present. Although the origin of the decreased basal glucose uptake remains unknown it might be related to a similar decrease in basal glucose uptake by ventromedial hypothalamic cells, an event presumably resulting in a tendency to hyperphagia. Decreased basal glucose uptake by soleus muscle of ob/ob mice might explain the hyperglycemia, and hence partly the hyperinsulinemia and excessive fat deposition of those animals.     

Dietary specific sugars for serum protein enzymatic glycosylation in man

All glycoprotein sugars can theoretically derive from glucose. However, dietary specific sugars could represent preferential substrates or have regulatory roles in enzymatic glycosylation. This hypothesis was tested in man using stable isotopes. Healthy subjects ingested different amounts (150, 300, or 550 mg) of artificially 13C-enriched sugar (galactose, mannose, or glucose) diluted in 200 mL water containing 50 g 13C-poor sucrose. 13C enrichment of expired CO2 was monitored for 8 hours during indirect calorimetry. Serum glycoproteins were precipitated and delipidated at various intervals. Glycoprotein neutral sugars were obtained by acidic hydrolysis, purified by ion-exchange chromatography, derivatized to alditol acetates, and analyzed by gas chromatography-isotope ratio mass spectrometry. The oxidation rate for galactose and mannose was slower than the rate for glucose. Total oxidation over the 8-hour period was less than 10% of the ingested amount of galactose or mannose. Galactose and mannose were readily incorporated into glycoprotein glycans, in the native form or after interconversion, despite ingestion of a large excess of sucrose: glycoprotein sugar 13C enrichment was strongly higher after 13C-galactose or 13C-mannose than after 13C-glucose. Thus, the metabolism of these three sugars appears to be different. Specific dietary sugars could represent a new class of non essential nutrients displaying interesting metabolic roles. This could have practical consequences especially in parenteral nutrition, where glucose is currently the only sugar available for metabolism.     

Dicarboxylate transport at the vacuolar membrane of the CAM plant Kalancho? daigremontiana: sensitivity to protein-modifying and sulphydryl reagents

Malate is widespread as a charge-balancing anion in plant vacuoles and plays a central role in nocturnal CO2 assimilation in crassulacean acid metabolism (CAM). To characterize the malate transport system at the vacuolar membrane of CAM plants, tonoplast vesicles were prepared from leaf mesophyll cells of the crassulacean plant Kalancho? daigremontiana. Dicarboxylate uptake, assayed by a membrane-filtration method using [14C]malate or [14C]succinate, displayed saturation kinetics with apparent Km values of 4.0 mM (malate) and 1.8 mM (succinate); competition experiments indicated that both anions were transported by the same system. Dicarboxylate uptake was stimulated severalfold by activation of the tonoplast H(+)-ATPase or H(+)-PPiase, an effect inhibitable by ionophore. Passive (non-energized) dicarboxylate uptake was sensitive to the sulphydryl reagents N-ethylmaleimide and p-chloromercuribenzene sulphonate, as well as to a range of protein modifiers. In particular, inhibition by pyridoxal phosphate was completely substrate-protectable, and that by phenylglyoxal partially so, thus implicating at least one lysine residue and perhaps also an arginine residue in the substrate-recognition site of the transport protein. The involvement of one or more critical lysine residue was supported by analysis of the initial phase of inhibition by pyridoxal phosphate: this showed pseudo-first-order kinetics with a reaction order of 1.03 +/- 0.13 and a Kd for substrate protection close to the apparent Km for dicarboxylate uptake.     

Methionine transport by pig colonic mucosa measured during early post-natal development

New-born pig proximal colon, incubated in vitro, transports methionine with a Km of 0-33 mM and a Vmax of 0-62 mumole cm-2h-1. There is still a net transport of methionine on day 4, but the Km now increases to 10 mM and the Vmax falls to 0-15 mumole cm-2h-1. There is no net transport of methionine across proximal colons taken from 10-day-old pigs. 2. The mean intramucosal concentration of methionine, following incubation in medium containing 1 mM methionine, is 7-18+/-0-8 mM for the new-born, 0-55+/-0-05 mM for the 4-day-old and 0-31+/-0-06 mM for the 10-day-old pig. 3. Both methionine and glucose cause an immediate increase in the short-circuit current of new-born and 1-day-old pig colons. The kinetics for this interaction with methionine gives a Km for methionine of 0-24 mM and a maximum effect of 27 muA cm-2. This effect is not seen in 4- or 10-day-old pigs. 4. Net Na+ transport across the new-born pig proximal colon, measured in the absence of methionine, is about three times that calculated from the measured short-circuit current. Methionine increases the mucosal to serosal flux of Na+ by an amount roughly equal to that predicted from the increase in short-circuit current. The ability of glucose and methionine to affect short-circuit current is lost by day 4. 5. Short-circuit current, measured in the absence of methionine or glucose, increases between day 1 and 2 of post-natal life. This increased electrogenicity is maintained for up to at least 10 days after birth. 6. The pig proximal colon has many of the properties of a small intestine at birth. It actively transports methionine and the presence of methionine stimulates the absorption of Na+. These effects could be physiologically important in the pig, where the normal absorptive function of the intestine is temporarily inhibited at birth by the intestinal transmission of immune globulins.     

Performance and cost-effectiveness of selective screening criteria for Chlamydia trachomatis infection in women. Implications for a national Chlamydia control strategy

At 9 mM glucose, experimental results show that mitochondrial phosphate depletion (induced by glucose phosphorylation, catalyzed by mitochondrial hexokinase) reduces the activities of the respiratory chain, oxidative phosphorylation, and glutaminase. Consequently, the 14C-lactate oxidation to 14CO2 is lowered in the presence of glucose. The fall of ATP level triggers a high aerobic glycolysis by deinhibiting fructose-6-P kinase. NADH, generated by enhanced glyceraldehyde-3-P dehydrogenase activity, increases the reducing power. Moreover, the lactate dehydrogenase (LDH) system is shifted toward lactate formation, while NAD+ is regenerated and the oligomycin-inhibited ATP production is replaced by the iodoacetate-inhibited ATP production. From 14CO2 production and lactate accumulation it is calculated that about 60% of 14C-glucose which disappears is channelled into extraglycolytic reactions. On the contrary, 82% of glucose below l mM is metabolized through non-glycolytic reactions. The pyruvate kinase-M2 (PK-M2) inhibition does not limit the glycolytic flow from 9 mM glucose, but it may cause sustained gluconeogenesis.     

Studies of lysophospholipids related to the hamster sperm acrosome reaction in vitro

1. One of the metabolic features of acquired immunodeficiency syndrome is increased tissue glucose uptake documented by euglycaemic-hyperinsulinaemic clamp studies, suggesting increased insulin sensitivity. However, these results may also be related to the confounding effect of increased non-insulin-mediated glucose uptake in acquired immunodeficiency syndrome, which will result in an erroneously presumed increased insulin sensitivity. To study the contribution of non-insulin-mediated glucose uptake to total tissue glucose uptake in acquired immunodeficiency syndrome, we conducted a hypoinsulinaemic clamp study in clinically stable human immunodeficiency virus-infected (Centers for Disease Control class IV) men (n = 7) and healthy subjects (n = 5). Glucose uptake was measured by a primed, continuous infusion of [3-3H]glucose in the postabsorptive state and during somatostatin-induced insulinopenia at euglycaemic (approximately 5.3 mmol/l) and hyperglycaemic (approximately 11 mmol/l) glucose concentrations. 2. Basal glucose concentration (patients, 5.2 +/- 0.1 mmol/l; control subjects, 5.3 +/- 0.1 mmol/l) and basal glucose tissue uptake (patients, 15.9 +/- 0.5 mumol min-1 kg-1 fat-free mass; control subjects, 15.2 +/- 0.4 mumol min-1 kg-1 fat-free mass) were not different between the two groups. 3. Euglycaemic glucose uptake during somatostatin infusion, reflecting non-insulin-mediated glucose uptake, decreased to 82 +/- 3% in patients and 78 +/- 2% in control subjects (not significant). Under hyperglycaemic (approximately 11 mmol/l) conditions with sustained insulinopenia, no differences in glucose uptake existed between the two groups (patients, 16.8 +/- 0.6 mumol min-1 kg-1 fat-free mass; control subjects, 16.1+/- 0.3 mumol min-1 kg-1 fat-free mass).(ABSTRACT TRUNCATED AT 250 WORDS)     

Distinct regions of frequent loss of heterozygosity of chromosome 5p and 5q in human esophageal cancer

Twenty strains of Streptococcus bovis grew more slowly on lactose (1.21 +/- 0.12 h-1) then than on glucose (1.67 +/- 0.12 h-1), and repeated transfers or prolonged growth in continuous culture (more than 200 generations each) did not enhance the growth rate on lactose. Lactose transport activity was poorly correlated with growth rate, and slow growth could not be explained by the ATP production rate (catabolic rate). Batch cultures growing on lactose always had less intracellular fructose 1,6-bisphosphate (Frul,6P2) than cells growing on glucose (6.6 mM compared to 16.7 mM), and this difference could be explained by the pathway of carbon metabolism. Glucose and the glucose moiety of lactose were metabolized by the Embden-Meyerhoff-Parnas (EMP) pathway, but the galactose moiety of lactose was catabolized by the tagatose pathway, a scheme that by-passed Frul,6P2. A mutant capable of co-metabolizing lactose and glucose grew more rapidly when glucose was added, even though the total rate of hexose fermentation did not change. Wild-type S. bovis grew rapidly with galactose and melibiose, but these galactose-containing sugars were activated by galactokinase and catabolized via EMP. On the basis of these results, rapid glycolytic flux through the EMP pathway is needed for the rapid growth (more than 1.2 h-1) of S. bovis.     

Pulmonary venoocclusive disease

The tortoise intestine capability for active transport of sugars has been studied in vitro at 30 degrees C, using labelled sugars. A release of glucose from the glycogen stores of the intestinal wall to the medium took place throughout the incubation period of the sacs. An active transport of 14C-D-glucose against a concentration gradient from the mucosal to the serosal compartment was evident, whereas no such activity could be detected for 14C-D-galactose. The tissue oxygen uptake was 36% higher with glucose than with galactose in the medium.     

Characterization of leucine transport by toadfish liver in vivo

Kinetic analysis of L-leucine uptake by toadfish liver at 20 degrees C in vivo has been carried out after pulse injection of L-[14C]leucine into the hepatic portal vein. D-[3H]mannitol, which is taken up slowly by toadfish liver, is used as a marker for extracellular space and space accessible by simple diffusion. At normal plasma leucine concentration (0.1 mM), leucine uptake occurs rapidly (t1/2 = 0.25 min), representing a flux of 0.6 mumol/min for the liver as a whole. Analysis of the distribution of radioactive leucine among intracellular and extracellular free pools and protein-bound form at times of 30 s to 5 min after injection is consistent with operation of a concentrative or uphill transport system accounting for 40% of uptake at normal plasma concentration. Saturation of uptake occurs at increasing leucine loads; calculation of intracellular pool dilution from protein synthesis data indicates that 20-30% of liver intracellular space is occupied by incoming leucine during the first 2 min after portal injection. Maximal flux (V max) is 4.1 mumol/min per 7-g liver as a whole with Km = 0.6 mM. Competitive inhibition of leucine uptake is afforded by isoleucine and phenylalanine with lesser effects by aspartic acid, cysteine, methionine, threonine, tyrosine, and valine. No effect is observed with alanine, glycine, histidine, lysine, and proline.     

Profound underestimation of glucose uptake by [18F]2-deoxy-2-fluoroglucose in reperfused rat heart muscle

BACKGROUND: [18F]2-deoxy-2-fluoroglucose (FDG) is widely used as a tracer for glucose uptake in ischemic heart muscle. We tested the effects of low-flow ischemia and reperfusion on the ratio of tracer/tracee (lumped constant, LC). METHODS AND RESULTS: Isolated working rat hearts were perfused with Krebs-Henseleit buffer containing only glucose 5 mmol/L (group 1) or glucose 5 mmol/L plus oleate 0.4 mmol/L (group 2, fed; group 3, fasted). Dynamic glucose uptake was measured simultaneously with [2-3H]glucose and with FDG. After 20 minutes, coronary flow was reduced by 75% for 30 minutes before it was returned to control conditions for the final 20 minutes. Hexokinase activity in the cytosolic and mitochondrial fractions and tissue metabolites were determined. Rates of glucose uptake were highest when glucose was the only substrate. Glucose uptake, FDG uptake, and the LC increased during ischemia only in group 3. There was no change of these parameters during ischemia in groups 1 and 2. FDG uptake decreased significantly with reperfusion in groups 2 and 3, and there was a striking fall in the LC (from >1.0 to <0.2, P<.001). The fall in the LC was associated with a significant increase in intracellular free glucose. Neither ischemia nor reperfusion affected the kinetic properties of hexokinase. CONCLUSIONS: FDG profoundly underestimates glucose uptake during reperfusion in the presence of fatty acids. In the fasted state, however, FDG overestimates glucose uptake during ischemia. The results indicate limitations in the use of FDG to quantify myocardial glucose uptake in human heart.