Endogenous Glucose Research Articles

Fructose-1,6-Bisphosphate and Fructose-2,6-Bisphosphate do not Influence Brain Carbohydrate or High-energy Phosphate Metabolism in a Rat Model of Forebrain Ischemia

Phosphorylated fructose compounds have been reported to lessen neuronal injury in in vitro models of hypoxia and in vivo models of ischemia. Although a variety of mechanisms have been proposed to account for this finding, it is unknown if intracellular uptake and incorporation of these compounds into the glycolytic pathway contribute to the benefit. We evaluated phosphorylated fructose administration in an adult rat model of transient, near-complete cerebral ischemia to determine its impact on brain metabolism before, during, and after ischemia. Fifty-four pentobarbital anesthetized rats were randomly assigned to receive IV infusions of either fructose-1,6-bisphosphate, fructose-2,6-bisphosphate, or 0.9% saline. After 2 hours of infusion, 18 rats (6/treatment group) were subjected to brain harvesting before any ischemia, 18 additional rats had brain harvesting at the completion of 10 minutes of forebrain ischemia (2-vessel occlusion plus induced hypotension), and 18 rats had harvesting after ischemia and 15 minutes of reperfusion. Cortical brain samples were analyzed for ATP, ADP, AMP, phosphocreatine, glucose, and glycogen. When compared with placebo, neither phosphorylated fructose compound altered preischemic, intraischemic, or postischemic concentrations of brain high-energy phosphates, glucose, glycogen, or lactate, nor did they influence the intraischemic metabolism of endogenous brain glucose or glycogen. On the basis of these results, we conclude that mechanisms other than augmented carbohydrate metabolism are responsible for previous reports of neuronal protection by the bisphosphonates.

Importance of changes in gastric emptying for postprandial plasma glucose fluxes in healthy humans

Regulation of postprandial (pp) plasma glucose excursions is complex. Insulin and glucagon are thought to play the predominant role. Nevertheless, only 50% of the variation in pp plasma glucose excursions is explained by variations by the latter. Theoretically, gastric emptying (GE) should be another important factor. However, its impact on pp glucose homeostasis is unknown. We examined the consequences of pramlintide-induced delay in GE on pp glycemia and glucose fluxes, determined isotopically. GE was recorded by scintigraphy. Fourteen healthy subjects (8 men, 6 women; age 40 +/- 3 yr, body mass index 27.8 +/- 1.1 kg/m2) ate a mixed meal, and 30 microg of pramlintide (PRAM) or placebo (PBO) were injected subcutaneously. At 60 min, greater proportions of the initial gastric contents remained in the stomach (PBO vs. PRAM). Thereafter, GE slopes paralleled until 240 min. Fifty percent retention times were lower when PBO was given (P < 0.001). GE was greater from 240 min to the end of the PRAM experiments, so that only slightly greater proportions of the meal remained in the stomach at 330 min. Reductions of GE lowered pp glucose (7.5 +/- 0.3 vs. 6.0 +/- 0.2 mmol/l, P < 0.001), even though plasma insulin was lower with PRAM (164 +/- 13 vs. 138 +/- 13 pmol/ml, both P < 0.01). Reduction in total glucose appearance (P < 0.001) was due to reduced meal-derived glucose appearance (10.2 +/- 0.5 vs. 7.0 +/- 0.4 micromol.kg(-1).min(-1), P < 0.001). Endogenous glucose appearance was greater with PRAM (P < 0.001). Splanchnic glucose uptake was greater with PRAM (26.5 +/- 1.6 vs. 32.5 +/- 2.1%, P = 0.014). These data support the concept that GE is an important physiological regulator of pp glucose homeostasis in humans.

Immunogold study of effects of prenatal exposure to lipopolysaccharide and/or valproic acid on the rat blood-brain barrier vessels

The involvement of blood microvessels, representing the anatomic site of the blood-brain barrier (BBB), in brain damage induced by prenatal exposure to lipopolysaccharide (LPS) and/or valproic acid (VPA) was studied in four-week-old rats. The immunogold procedure was applied for localization at the ultrastructural level of endogenous albumin and glucose transporter (GLUT-1) in three brain regions: cerebral cortex, cerebellum and hippocampus. Four groups of rats were used: (1) untreated control, (2) prenatally VPA-treated, (3) prenatally LPS-treated, and (4) prenatally LPS- and VPA-treated. The functional state of the BBB was evaluated as follows: (a) by its tightness, i.e., permeability to blood-borne albumin, and (b) by the expression of GLUT-1 in the endothelial cells (ECs). Using morphometry, the labelling density for GLUT-1 was recorded over luminal and abluminal plasma membranes of the ECs, also providing information on their functional polarity. No extensive increase of vascular permeability and/or any considerable dysfunction of the BBB in experimental groups nos. 2 and 3 were observed, although in solitary vascular profiles, increased endocytosis or even transcytosis of albumin by ECs was noted. In experimental group no. 4, some vascular profiles showed scanty leakage (microleakage), manifested by the presence of immunosignals for albumin in the perivascular area. Although some fluctuations in the expression of GLUT-1 occurred in all experimental groups, especially in group no. 3, a most pronounced and significant diminution of the labelling density, in all three regions of the brain, was observed in group no. 4. This finding suggests the synergistic action of prenatally applied LPS and VPA that affects specific transport functions of glucose in the microvascular endothelium. The diminished or disturbed supply of glucose to selected brain regions can be one of the factors leading to previously observed behavioral disturbances in similarly treated rats.

Amperometric, screen-printed, glucose biosensor for analysis of human plasma samples using a biocomposite water-based carbon ink incorporating glucose oxidase

This paper describes the optimisation of a screen-printing water-based carbon ink containing cobalt phthalocyanine (CoPC) and glucose oxidase (GOD) for the fabrication of a glucose biosensor. To optimise the performance of the biosensor, the loadings of the electrocatalyst (CoPC) and enzyme (GOD) were varied. It was found that the maximum linear range was achieved with a CoPC loading of 20% (m/m, relative to the mass of carbon) and a GOD loading of 628 U per gram of carbon. In our studies we chose to employ chronoamperometry, as this technique is commonly used for commercial devices. The optimum operating applied potential was found to be +0.5 V, following an incubation period of 60 s. The optimum supporting electrolyte was found to be 0.05 M phosphate buffer at pH 8.0, which resulted in a linear range of 0.2–5 mM, the former represents the detection limit. The sensitivity was 1.12 μA mM −1. The effect of temperature was also investigated, and it was found that 40 °C gave optimal performance. The resulting amperometric biosensors were evaluated by measuring the glucose concentrations for 10 different human plasma samples containing endogenous glucose and also added glucose. The same samples were analysed by a standard spectrophotometric method, and the results obtained by the two different methods were compared. A good correlation coefficient ( R 2 = 0.95) and slope (0.98) were calculated from the experimental data, indicating that the new devices hold promise for biomedical studies.

Reduction in Muscle Glycogen and Protein Utilization with Glucose Feeding during Exercise

Effects of feeding glucose on substrate metabolism during cycling were studied. Trained (60.0 +/- 1.9 mL x kg(-1) x min(-1)) males (N = 5) completed two 75 min, 80% VO(2max) trials: 125 g 13(C)-glucose CHO); 13(C)-glucose tracer, 10 g (C). During warm-up (30 min 30% VO2max) 2 . 2 g 13(C)-glucose was given as bicarbonate pool primer. Breath samples and blood glucose were analyzed for 13(C/12)C with IRMS. Protein oxidation was estimated from urine and sweat urea. Indirect calorimetry (protein corrected) and 13(C/12)C enrichment in expired CO(2)and blood glucose allowed exogenous (Gexo), endogenous (Gendo), muscle (Gmuscle), and liver glucose oxidation calculations. During exercise (75 min) in CHO versus C (respectively): protein oxidation was lower (6.8 +/- 2.7, 18.8 +/- 5.9 g; P = 0.01); Gendo was reduced (71.2 +/- 3.8, 80.7 +/- 5.7% P = 0.01); Gmuscle was reduced (55.3 +/- 6.1, 65.9 +/- 6.0%; P = 0.01) compensated by increased Gexo(58.3 +/- 2.1, 3.87 +/- 0.85 g; P = 0.000002). Glucose ingestion during exercise can spare endogenous protein and carbohydrate, in fed cyclists, without glycogen depletion.

Time-course changes in macronutrient metabolism induced by a nutritionally balanced low-calorie diet in obese women

The use of low-calorie diets is a common strategy for body-weight reduction purposes, but the time-course of the metabolic changes induced by moderately energy-restricted, otherwise balanced, diets is still poorly known. The aim of this nutritional intervention design was to study in obese women the effect of a balanced low-calorie diet on the metabolic rate, and metabolic fuel utilization changes during the weight loss process through the application of breath tests with stable isotope-labeled tracers.Seven obese (body mass index >30 kg/m2) women were assigned to a 10-week dietary hypoenergetic intervention regime supplying 55% of energy as carbohydrate, 30% as fat and 15% as protein. Metabolic rate and substrate utilization were evaluated for 6 h in separate occasions during the weight loss program by indirect calorimetry and after 13C-labeled glucose, triolein and leucine administration. Body weight loss after 10 weeks was 4.2±1.1 kg, while the percent body fat decrease was about 5%. Slimming was accompanied by a marked decrease in fasting leptin (about 25%). Postprandial carbohydrate utilization after the administration of a test meal with the same macronutrient distribution as the experimental low-energy diet was decreased (24.1%, P<0.05) as a consequence of the dietary restriction, which was associated with lower insulin plasma levels (P<0.05). Although protein and lipid oxidation were not significantly different after weight reduction (day 1 versus day 70), the metabolic utilization of these substrates tended to increase. Moreover, marginally significant indications obtained on days 15 and 45 suggest that the weight and body composition changes are attributable to a shift in endogenous and exogenous glucose utilization in favor of lipid burning. The breath tests determinations, which were performed on different occasions along the experimental trial, confirmed that the cumulative 13C output decreased for labeled tracers with time, being only statistically significant for the glucose utilization between days 15 and 45. In summary, the weight and fat mass losses were associated with a lower carbohydrate oxidation, which were probably compensated by an increase in lipid oxidation without major changes in protein mobilization.

Nonesterified fatty acids and hepatic glucose metabolism in the conscious dog.

We used tracer and arteriovenous difference techniques in conscious dogs to determine the effect of nonesterified fatty acids (NEFAs) on net hepatic glucose uptake (NHGU). The protocol included equilibration ([3-(3)H]glucose), basal, and two experimental periods (-120 to -30, -30 to 0, 0-120 [period 1], and 120-240 min [period 2], respectively). During periods 1 and 2, somatostatin, basal intraportal insulin and glucagon, portal glucose (21.3 micromol.kg(-1).min(-1)), peripheral glucose (to double the hepatic glucose load), and peripheral nicotinic acid (1.5 mg.kg(-1).min(-1)) were infused. During period 2, saline (nicotinic acid [NA], n = 7), lipid emulsion (NA plus lipid emulsion [NAL], n = 8), or glycerol (NA plus glycerol [NAG], n = 3) was infused peripherally. During period 2, the NA and NAL groups differed (P < 0.05) in rates of NHGU (10.5 +/- 2.08 and 4.7 +/- 1.9 micromol.g(-1).min(-1)), respectively, endogenous glucose R(a) (2.3 +/- 1.4 and 10.6 +/- 1.0 micromol.kg(-1).min(-1)), net hepatic NEFA uptakes (0.1 +/- 0.1 and 1.8 +/- 0.2 micromol.kg(-1).min(-1)), net hepatic beta-hydroxybutyrate output (0.1 +/- 0.0 and 0.4 +/- 0.1 micromol.kg(-1).min(-1)), and net hepatic lactate output (6.5 +/- 1.7 vs. -2.3 +/- 1.2 micromol.kg(-1).min(-1)). Hepatic glucose uptake and release were 2.6 micro mol. kg(-1). min(-1) less and 3.5 micro mol. kg(-1). min(-1) greater, respectively, in the NAL than NA group (NS). The NAG group did not differ significantly from the NA group in any of the parameters listed above. In the presence of hyperglycemia and relative insulin deficiency, elevated NEFAs reduce NHGU by stimulating hepatic glucose release and suppressing hepatic glucose uptake.

Insulin secretion and insulin sensitivity in normal pregnancy and gestational diabetes mellitus

The purpose of this study was to evaluate insulin sensitivity ,β-cell function and islet-cell-directed autoimmunity in pregnant women with normal glucose tolerance and gestational diabetes mellitus(GDM). A total of 21 women with normal glucose tolerance and 21 women with GDM were evaluated at 24-36 weeks' gestation. Insulin resistance and β-cell function were evaluated using the continuous infusionof glucose with model assessment (CIGMA) method ,which aims to give a near-physiological stimulus and to evaluate the endogenous insulin and glucose response. Islet-cell autoantibody was positive in onewoman with GDM ,and glutamic acid decarboxylase autoantibodies were negative in both groups. The calculated CIGMA insulin resistance (CIGMA IR) was 2.04 ± 1.74 and 1.08 ± 1.22 in patientswith GDM and in control subjects ,respectively (p < 0.05). CIGMA percentage β-cell values were 64.04 ± 44.55% and 87.07 ± 52.77% in patients with GDM and control subjects ,respectively(p > 0.05). Decreased insulin sensitivity in late pregnancy was more evident in lean GDM subjects with mild hyperglycemia who did not require insulin therapy ,and β-cell function was partially preservedin this group of patients.

Prior exercise and the response to insulin-induced hypoglycemia in the dog.

To test whether hepatic insulin action and the response to an insulin-induced decrement in blood glucose are enhanced in the immediate postexercise state as they are during exercise, dogs had sampling (artery, portal vein, and hepatic vein) catheters and flow probes (portal vein and hepatic artery) implanted 16 days before a study. After 150 min of moderate treadmill exercise or rest, dogs were studied during a 150-min hyperinsulinemic (1 mU.kg(-1).min(-1)) euglycemic (n = 5 exercised and n = 9 sedentary) or hypoglycemic (65 mg/dl; n = 8 exercised and n = 9 sedentary) clamp. Net hepatic glucose output (NHGO) and endogenous glucose appearance (R(a)) and utilization (R(d)) were assessed with arteriovenous and isotopic ([3-(3)H]glucose) methods. Results show that, immediately after prolonged, moderate exercise, in relation to sedentary controls: 1) the glucose infusion rate required to maintain euglycemia, but not hypoglycemia, was higher; 2) R(d) was greater under euglycemic, but not hypoglycemic conditions; 3) NHGO, but not R(a), was suppressed more by a hyperinsulinemic euglycemic clamp, suggesting that hepatic glucose uptake was increased; 4) a decrement in glucose completely reversed the enhanced suppression of NHGO by insulin that followed exercise; and 5) arterial glucagon and cortisol were transiently higher in the presence of a decrement in glucose. In summary, an increase in insulin action that was readily evident under euglycemic conditions after exercise was abolished by moderate hypoglycemia. The means by which the glucoregulatory system is able to overcome the increase in insulin action during moderate hypoglycemia is related not to an increase in R(a) but to a reduction in insulin-stimulated R(d). The primary site of this reduction is the liver.

Novel Peptides under Development for the Treatment of Type 1 and Type 2 Diabetes Mellitus

Recent availability of expanded treatment options for both type 1 and type 2 diabetes has not translated into easier and significantly better glycemic and metabolic management. Patients with type 1 diabetes continue to experience increased risk of hypoglycemic episodes and progressive weight gain resulting from intensive insulin treatment, despite the recent availability of a variety of insulin analog. Given the progressive nature of the disease, most patients with type 2 diabetes inevitably proceed from oral agent monotherapy to combination therapy and, ultimately, require exogenous insulin replacement. Insulin therapy in type 2 diabetes is also accompanied by untoward weight gain. Both type 1 and type 2 diabetes continue to be characterized by marked postprandial hyperglycemia. Two hormones still in development are candidates for pharmacologic intervention, have novel modes of action (some centrally mediated), and show great promise in addressing some of the unmet needs of current diabetes management. Pramlintide acetate, an analog of the beta cell hormone amylin and the first non-insulin related therapeutic modality for type 1 and type 2 diabetic patients with severe beta cell failure, may be useful as adjunctive therapy to insulin. The principal anti-diabetic effects of pramlintide arise from interactions via its cognate receptors located in the central nervous system resulting in postprandial glucagon suppression, modulation of nutrient absorption rate, and reduction of food intake. Another polypeptide hormone, exendin-4, exerts at least some of its pharmacologic actions as an agonist at the glucagon-like peptide-1 (GLP-1) receptor. GLP-1 and related compounds exhibit multiple modes of action, the most notable being a glucose-dependent insulinotropic effects and the pote ntial to preserve or improve the beta-cell function. The latter effect could potentially halt or delay the progressive deterioration of the diabetic state associated with type 2 diabetes. Physiologically, both amylin and glucagon-like peptide (GLP)-1, along with insulin, are involved in a coordinated and concerted interplay between hormones acting both centrally and peripherally to provide meticulous control over the rate of appearance of exogenous and endogenous glucose and to match that rate to the rate of glucose disappearance. Both hormones are deficient in diabetes. Therapies directed at restoring this complex physiology have the potential to facilitate glucose control and thus minimize the attendant complications of diabetes Keywords: glucagon-like peptide(glp), exendin-4

Novel Peptides under Development for the Treatment of Type 1 and Type 2 Diabetes Mellitus

Recent availability of expanded treatment options for both type 1 and type 2 diabetes has not translated into easier and significantly better glycemic and metabolic management. Patients with type 1 diabetes continue to experience increased risk of hypoglycemic episodes and progressive weight gain resulting from intensive insulin treatment, despite the recent availability of a variety of insulin analog. Given the progressive nature of the disease, most patients with type 2 diabetes inevitably proceed from oral agent monotherapy to combination therapy and, ultimately, require exogenous insulin replacement. Insulin therapy in type 2 diabetes is also accompanied by untoward weight gain. Both type 1 and type 2 diabetes continue to be characterized by marked postprandial hyperglycemia. Two hormones still in development are candidates for pharmacologic intervention, have novel modes of action (some centrally mediated), and show great promise in addressing some of the unmet needs of current diabetes management. Pramlintide acetate, an analog of the beta cell hormone amylin and the first non-insulin related therapeutic modality for type 1 and type 2 diabetic patients with severe beta cell failure, may be useful as adjunctive therapy to insulin. The principal anti-diabetic effects of pramlintide arise from interactions via its cognate receptors located in the central nervous system resulting in postprandial glucagon suppression, modulation of nutrient absorption rate, and reduction of food intake. Another polypeptide hormone, exendin-4, exerts at least some of its pharmacologic actions as an agonist at the glucagon-like peptide-1 (GLP-1) receptor. GLP-1 and related compounds exhibit multiple modes of action, the most notable being a glucose-dependent insulinotropic effects and the potential to preserve or improve the beta-cell function. The latter effect could potentially halt or delay the progressive deterioration of the diabetic state associated with type 2 diabetes. Physiologically, both amylin and glucagon-like peptide (GLP)-1, along with insulin, are involved in a coordinated and concerted interplay between hormones acting both centrally and peripherally to provide meticulous control over the rate of appearance of exogenous and endogenous glucose and to match that rate to the rate of glucose disappearance. Both hormones are deficient in diabetes. Therapies directed at restoring this complex physiology have the potential to facilitate glucose control and thus minimize the attendant complications of diabetes.

Effect of prior exercise on glucose metabolism in trained men

Several studies have demonstrated that oral glucose tolerance is impaired in the immediate postexercise period. A double-tracer technique was used to examine glucose kinetics during a 2-h oral glucose (75 g) tolerance test (OGTT) 30 min after exercise (Ex, 55 min at 71 +/- 2% of peak O(2) uptake) and 24 h after exercise (Rest) in endurance-trained men. The area under the plasma glucose curve was 71% greater in Ex than in Rest (P = 0.01). The higher glucose response occurred even though whole body rate of glucose disappearance was 24% higher after exercise (P = 0.04, main effect). Whole body rate of glucose appearance was 25% higher after exercise (P = 0.03, main effect). There were no differences in total (2 h) endogenous glucose appearance (R(a)E) or the magnitude of suppression of R(a)E, although R(a)E was higher from 15 to 30 min during the OGTT in Ex. However, the cumulative appearance of oral glucose was 30% higher in Ex (P = 0.03, main effect). There were no differences in glucose clearance rate or plasma insulin responses between the two conditions. These results suggest that adaptations in splanchnic tissues by prior exercise facilitate greater glucose output from the splanchnic region after glucose ingestion, resulting in a greater glycemic response and, consequently, a greater rate of whole body glucose uptake.

Glucose ingestion and substrate utilization during exercise in boys with IDDM.

This study was intended to compare exogenous [(13)C]glucose (Glu(exo)) oxidation in boys with insulin-dependent diabetes mellitus (IDDM) and healthy boys of similar age, weight, and maximal O(2) uptake. In a control trial with water intake (CT) and in a (13)C-enriched glucose trial (GT), subjects cycled for 60 min (58.8 +/- 0.9% maximal O(2) uptake) while the utilization of total glucose, total fat, and Glu(exo) was assessed. In CT, total glucose was 84.7 +/- 9.2 vs. 91.3 +/- 6.6 g/60 min (not significantly different) and total fat was 13.3 +/- 2.2 vs. 11.1 +/- 1.7 g/60 min (not significantly different) in IDDM vs. healthy boys, respectively. In GT, Glu(exo) was 10.4 +/- 1.7 vs. 14.8 +/- 1.1 g/60 min, corresponding to 9.0 +/- 1.0 vs. 12.4 +/- 0.5% of the total energy supply in IDDM and healthy boys, respectively (P < 0.05). Endogenous glucose was spared in both groups by 12.6 +/- 3.5% (P < 0.05). Blood glucose and plasma insulin concentrations were two- to threefold higher in IDDM vs. healthy boys in both trials. In conclusion, Glu(exo) is impaired in exercising boys with IDDM, even when plasma insulin levels are elevated.

A blood test for intestinal permeability and function: A new tool for the diagnosis of chronic intestinal disease in dogs

We demonstrate that rhamnose, 3-O-methyl-d-glucose, d-xylose and lactulose may be quantified accurately in blood by HPLC and pulsed amperometric detection, thus enabling studies of intestinal permeability and function to be carried out using plasma samples. Prior to HPLC, the endogenous glucose was enzymatically modified to gluconic acid and the protein precipitated. The precision of the quantification of the sugars in plasma (C.V.: 2.2–5.7%; 8.7–10.6% at very low concentrations) compared well with the quantification in urine. The results for groups of 8 dogs with small intestinal bacterial overgrowth and 12 dogs with inflammatory bowel disease were shown to be significantly different from a group of 20 normal control dogs (P<0.001), demonstrating the test's value as a diagnostic tool. The normal ranges in blood 2 h post oral administration were determined to be 0.05–0.17 for the lactulose/rhamnose ratio and 0.45–0.65 for the xylose/3-O-methylglucose ratio. This method may be employed advantageously when the collection of urine in intestinal permeability and function tests is difficult.

Effects of metformin on the pathways of glucose utilization after oral glucose in non—insulin-dependent diabetes mellitus patients

To analyze the effects of metformin (M) on the kinetics and pathways of glucose utilization after glucose ingestion, nine non-insulin-dependent diabetes mellitus (NIDDM) patients underwent two 5-hour oral glucose tolerance tests (OGTTs) preceded in random order by a 3-week treatment with either M (850 mg twice per day) or placebo. Each test included intravenous infusion of 3- 3H-glucose and labeling of the oral dose (75 g) with 1- 14C-glucose, with measurements of glucose kinetics, glycolytic flux ( 3H 2O production), and glucose oxidation (indirect calorimetry and expired 14CO 2). Basal glycemia was decreased by M (6.6 v 8.2 mmol/L, P < .01) with no changes in insulin levels, with the hypoglycemic effect correlating strongly ( P < .001) with a decrease in glucose production. Mean 0- to 5-hour postprandial glycemia was also decreased by the drug (9.9 v 12.2 mmol/L, P < .04), lactate concentration was increased (1.79 v 1.44 mmol/L, P < .01), and absolute insulin levels were increased, but not to a significant extent. The rates of appearance (Ra) of exogenous and endogenous glucose were not modified, and the hypoglycemic effect of M in the postprandial state was entirely related to an increase in systemic glucose disposal (85.1 v 77.5 g/5 h, P < .001). Carbohydrate oxidation was unchanged, and glycolytic flux and nonoxidative glycolysis were increased by approximately 13 g/5 h ( P < .01), with the excess lactate produced probably being converted to glycogen in the liver. Whole-body glycogen synthesis through the direct pathway tended to be reduced (−8 g/5 h, P > .05). Thus, M decreases postprandial glycemia by increasing glucose disposal and stimulates lactate production. The data also suggest that the drug increases the proportions of glycogen deposited through the indirect rather than the direct pathway.

Purification and characterization of encystment-inducedglucosamine 6-phosphate isomerase in Giardia

Giardia intestinalis encystment results in the incorporation of galactosamine (GalN) (a cyst- wall specific sugar) into outer cyst wall filaments [1,2]. GalN is synthesized during encystment from endogenous glucose by an inducible enzyme pathway [3] and the first reaction unique to GalN synthesis is the conversion of fructose-6-phosphate (F6P) to glucosamine 6-phosphate (G1cN6P) [4,5].

Gemfibrozil treatment of endogenous hypertriglyceridemia: effect on insulin-mediated glucose disposal and plasma insulin concentrations.

Gemfibrozil or placebo was administered for 3 months to 24 individuals with endogenous hypertriglyceridemia and normal glucose tolerance. Mean ( +/- SEM) fasting plasma triglyceride (TG) concentrations decreased (4.01 +/- 0.55 to 1.34 +/- 0.12 mmol/L; P < 0.001) and high density lipoprotein cholesterol concentrations increased (0.54 +/- 0.03 to 0.67 +/- 0.04 mmol/L; P < 0.001) in gemfibrozil-treated patients, associated with lower (P < 0.01-0.001) plasma free fatty acid and TG concentrations when measured at hourly intervals in response to breakfast (0800 h) and lunch (1200 h). However, day-long plasma glucose and insulin responses to meals in the 2 groups were similar before and after treatment, as were the steady state plasma glucose and insulin concentrations at the end of a 180-min infusion of somatostatin, insulin, and glucose. Thus, marked decreases in both plasma TG and free fatty acid concentrations seen in association with gemfibrozil neither enhanced insulin-mediated glucose disposal nor lowered ambient plasma insulin concentrations in patients with endogenous hypertriglyceridemia.

Influence of exogenous abscisic acid on germination and plantlet conversion frequencies of hybrid larch somatic embryos (Larix � leptoeuropaea)

The effect of exogenous abscisic acid, provided to somatic embryos during the maturation step, on endogenous abscisic acid and its main conjugated form (abscisic acid glucose ester), germination and conversion frequencies is presented in this paper. Abscisic acid measurements were obtained after a methanolic extraction, a fractionation through high performance liquid chromatography, quantitation with an immunoassay and identification of the quantitated compound using gas chromatography-mass spectrometry. Results show that endogenous abscisic acid and abscisic acid glucose ester levels are clearly correlated with the exogenous abscisic acid concentration provided to the embryos. Maturation was clearly enhanced by exogenous abscisic acid, but no correlation was found between abscisic acid concentration and germination frequency. Conversely, development of the aerial part of the germinated somatic embryos was dependent upon the abscisic acid concentration in the culture medium and results suggest that this dependence could be related to the endogenous abscisic acid content.

Sucrose application causes hormonal changes associated with potato tuber induction

Stems of potato plants (Solanum tuberosum L. cv. Dianella) were immersed in solutions containing water (control), sucrose, glucose, paclobutrazol, and gibberellic acid. The effects of these treatments on the ethylene release, levels of endogenous gibberellins, glucose, sucrose, and starch were correlated with tuberization of nodal cuttings, excised from potato stems. Paclobutrazol and sucrose improved the percent of tuberization and/or increased tuber weight. In contrast, GA3 inhibited tuber formation compared with the control. The level of endogenous free GAs was negatively correlated with percent tuberization. However, the level of conjugated GAs was positively correlated with both percent tuberization and tuber weight. The effect of sucrose on potato tuber induction in relation to the possible role of sucrose in GA-conjugate formation is discussed.

Development of Glucose Utilization Studied in Single Oocytes and Preimplantation Embryos from Mice1

Superovulated mouse oocytes and embryos were isolated and incubated with nontracer concentrations of 2-deoxyglucose, an analog of glucose, which is transported into the cells by glucose transporter and phosphorylated by hexokinase to 2-deoxyglucose 6-phosphate; it is not rapidly metabolized further, and accumulates in the cytosol. Using our non-radiometric and enzymatic microassay method, we determined 2-deoxyglucose and 2-deoxyglucose 6-phosphate amounts in individual oocytes and preimplantation embryos after the incubation. Hexokinase activity increased continuously and exponentially during development from follicular oocytes to blastocysts. Endogenous glucose and glucose 6-phosphate decreased precipitously from follicular oocytes to unfertilized and ovulated oocytes. Fertilization induced rapid increases in glucose and glucose 6-phosphate concentrations, which increased exponentially thereafter during embryonic development. 2-Deoxyglucose incorporation and 2-deoxyglucose 6-phosphate formation were undetectable in unfertilized oocytes. However, when cumulus-oocyte complexes were incubated with 2-deoxyglucose, 2-deoxyglucose was incorporated into cumulus cells surrounding follicular oocytes and transported via the gap junctions into the follicular oocytes. Fertilization triggered facilitative 2-deoxyglucose transport in one-cell embryos, and the capacities of 2-deoxyglucose incorporation and 2-deoxyglucose 6-phosphate formation developed along with the maturation of preimplantation embryos.