Differences In Glucose Utilization Research Articles

Evaluation of platelet additive solution for prolonging storage of functional canine platelet concentrate.

To assess storage lesion development, platelet function, and bacterial growth in canine platelet concentrates (PCs) stored in a platelet additive solution (PAS) or a plasma control at 4°C for 21days. Prospective, ex vivo, experimental controlled study. University veterinary teaching hospital. Ten units of canine PCs collected from blood bank donations. The PCs were separated into 2 bags, 1 containing 100% plasma and the other containing 35% plasma and 65% of a PAS (Plasma-Lyte A), and stored at 4°C for 21days. At days 0, 7, 14, and 21, PCs were analyzed for the presence of swirling, aggregate formation, platelet counts, platelet indices, glucose, lactate, lactate dehydrogenase, Pvco2 , Pvo2 , aggregation via light aggregometry, activation percentages using flow cytometry, and bacterial growth. Cold-stored PCs in both PAS and plasma control maintained mean pH >6.8 and mean lactate <9.0mmol/L over 21days, with no difference in glucose utilization. Swirl was maintained in both solutions for most days (76/80 combined total samples), with no difference in aggregate formation between solutions. The Pvco2 was higher in plasma on all days (P<0.001), with no difference in Pvo2 . Platelet indices did not reflect significant storage lesion development in either solution. Lactate dehydrogenase did not differ between solutions but did increase from day 7 to day 21. Mean maximal aggregation percentage was reduced overall but with no significant difference between solutions. The only observed difference in mean activation percentage between solutions was in PAS on day 7, which was significantly higher than plasma (P<0.05). No bacterial growth occurred during storage. Cold storage in PAS and plasma allowed PCs to be stored for up to 21days with minimal storage lesion development, maintenance of platelet function, limited platelet activation, and no bacterial growth within stored bags.

Differential regulation of nucleus accumbens glutamate and GABA in obesity-prone and obesity-resistant rats.

Obesity is one of the leading health concerns in the United States. Studies from human and rodent models suggest that inherent differences in the function of brain motivation centers, including the nucleus accumbens (NAc), contribute to overeating and thus obesity. For example, there are basal enhancements in the excitability of NAc GABAergic medium spiny neurons (MSN) and reductions in basal expression of AMPA-type glutamate receptors in obesity-prone vs obesity-resistant rats. However, very little is known about the regulation of extracellular glutamate and GABA within the NAc of these models. Here we gave obesity-prone and obesity-resistant rats stable isotope-labeled glucose (13 C6 -glucose) and used liquid chromatography mass spectrometry (LC-MS) analysis of NAc dialysate to examine the real-time incorporation of 13 C6 -glucose into glutamate, glutamine, and GABA. This novel approach allowed us to identify differences in glucose utilization for neurotransmitter production between these selectively bred lines. We found that voluntarily ingested or gastrically infused 13 C6 -glucose rapidly enters the NAc and is incorporated into 13 C2 -glutamine, 13 C2 -glutamate, and 13 C2 -GABA in both groups within minutes. However, the magnitude of increases in NAc 13 C2 -glutamine and 13 C2 -GABA were lower in obesity-prone than in obesity-resistant rats, while basal levels of glutamate were elevated. This suggested that there may be differences in the astrocytic regulation of these analytes. Thus, we next examined NAc glutamine synthetase, GAD67, and GLT-1 protein expression. Consistent with reduced 13 C2 -glutamine and 13 C2 -GABA, NAc glutamine synthetase and GLT-1 protein expression were reduced in obesity-prone vs obesity-resistant groups. Taken together, these data show that NAc glucose utilization differs dramatically between obesity-prone and obesity-resistant rats, favoring glutamate over GABA production in obesity-prone rats and that reductions in NAc astrocytic recycling of glutamate contribute to these differences. These data are discussed in light of established differences in NAc function between these models and the role of the NAc in feeding behavior.

GLP-1 responds to postprandial hyperglycemia by reducing transcription level in grass carp (Ctenopharyngodon idella)

Glucagon-like peptide-1 (GLP-1), a member of the proglucagon derived peptide family, is a highly effective incretin to reduce plasma glucose and inhibit food intake in mammals. The physiological function of GLP-1 has been elucidated in some ‘glucose intolerant’ carnivorous fishes. To lay a better understanding in fish glucose intolerance, we synthesized homologous GLP-1 peptide and explored its roles in appetite and glucose regulation under intraperitoneal (IP) injection in herbivorous grass carp which has higher glucose intolerance. The results showed that GLP-1 increased plasma glucose in grass carp. The hyperglycemic effect of the fish GLP-1 was mainly through promoting gluconeogenesis, accompanied by inhibition of glycogen synthesis and stimulation of glycogenolysis pathway. In addition, GLP-1 upregulated the expression of anorexigenic gene (cart) and decreased the orexigenic genes (npy and agrp) expression in grass carp hypothalamus as a conservative way to inhibit the appetite under GLP-1 injection after 2 h. Taken together, the hyperglycemic effect and anorectic role of GLP-1 were performed in a basically consistent manner across fishes with different food habits. What’s more, the gene expressions of proglucagon yielded GLP-1 in foregut and hindgut of grass carp were significantly decreased after a meal within 24 h, indicating that fish might suppress the accumulation of plasma glucose by decreasing GLP-1 expression in a unique way to herbivorous fish. Therefore, this study provided a new perspective for illustrating the difference in glucose utilization among fishes with different food habits based on GLP-1.

Exploring the Obesity Paradox in A Murine Model of Sepsis: Improved Survival Despite Increased Organ Injury in Obese Mice.

Despite the known deleterious effects of obesity, clinical data indicate that overweight or obese patients experience higher rates of sepsis survival compared to normal and underweight patients; a phenomenon called the obesity paradox. Results from preclinical sepsis studies have not been able to replicate these findings. The objective of this study was to test the existence of the obesity paradox in a murine model of cecal slurry (CS)-induced sepsis with insulin-resistant diet-induced obese mice. Male C57BL/6 mice were provided high-fat (HFD) or low-fat (LFD) diets for 20 weeks. HFD-fed mice experienced higher rates of survival compared to LFD-fed mice after septic challenge induced by CS injection (66% vs. 25%, P = 0.01, survival assessed for 14 days). Despite the survival advantage, HFD-fed mice had higher rates of positive bacterial cultures and increased markers of kidney injury. Circulating levels of IL-6, IL-1β, TNFα, and IL-23 were equivalent 24 h after CS-injection; however, IL-17A was uniquely increased in HFD-fed mice. While LFD-fed mice maintained euglycemia, HFD-fed mice were hyperglycemic 6 and 12 h after CS-injection. Stable isotope resolved metabolomics analysis of liver tissue showed diverging pathways of glucose utilization during sepsis, with LFD-fed mice significantly upregulating glycolytic activity and HFD-fed mice decreasing glucose entry into the TCA cycle. This murine study corroborates clinical data that obesity confers a survival benefit in sepsis, albeit at the expense of more significant organ injury. The mechanisms promoting survival in the obese remain unknown; however, this model appears to be well-poised to begin answering this question. Differences in glucose utilization are a novel target to investigate this paradox.

Placental Glucose Uptake in a Nonhuman Primate Model of Western-Style Diet Consumption and Chronic Hyperandrogenemia Exposure.

We reported that consumption of a western-style diet (WSD) with and without hyperandrogenemia perturbed placental perfusion and altered levels of glucose transporter proteins in rhesus macaques. Based on that result, we hypothesized that placental glucose uptake would be dysregulated in this model. In this study, female rhesus macaques were assigned at puberty to one of four groups: subcutaneous cholesterol implants + standard chow diet (controls, C); testosterone implants + chow (T); cholesterol implants + a high-fat, WSD; and T+WSD. After ~6 years of treatment, animals were mated, and pregnancies were delivered by cesarean section at gestational day (G) 130 (the term is G168). Placental villous explants were immediately prepared for radiolabeled glucose assay. Linear glucose uptake was observed between 0 and 30 s. At 20 s, glucose uptake in placental villous explants did not differ across the four treatment groups with values as follows: C: 25.5 ± 6.33, T: 22.9 ± 0.404, WSD: 26.9.0 ± 3.71, and T+WSD: 33.0 ± 3.12 (mean ± SD expressed in pmol/mg). Unlike our prior experiment, glucose transporter expression was reduced in WSD placentas, and our in vitro functional assay did not demonstrate a difference in glucose uptake across the transporting epithelium of the placenta. Notably, maternal blood glucose levels were significantly elevated in animals chronically fed a WSD. This disparity may indicate differences in glucose utilization and metabolism by the placenta itself, as glucose transporter expression and circulating fetal glucose concentrations were comparable across all four groups in this pregnancy cohort.

In Vivo Metabolism of [1,6-13C2]Glucose Reveals Distinct Neuroenergetic Functionality between Mouse Hippocampus and Hypothalamus.

Glucose is a major energy fuel for the brain, however, less is known about specificities of its metabolism in distinct cerebral areas. Here we examined the regional differences in glucose utilization between the hypothalamus and hippocampus using in vivo indirect 13C magnetic resonance spectroscopy (1H-[13C]-MRS) upon infusion of [1,6-13C2]glucose. Using a metabolic flux analysis with a 1-compartment mathematical model of brain metabolism, we report that compared to hippocampus, hypothalamus shows higher levels of aerobic glycolysis associated with a marked gamma-aminobutyric acid-ergic (GABAergic) and astrocytic metabolic dependence. In addition, our analysis suggests a higher rate of ATP production in hypothalamus that is accompanied by an excess of cytosolic nicotinamide adenine dinucleotide (NADH) production that does not fuel mitochondria via the malate-aspartate shuttle (MAS). In conclusion, our results reveal significant metabolic differences, which might be attributable to respective cell populations or functional features of both structures.

1749-P: The TNFa Inhibitor Infliximab Decreases Inflammation in High-Fat Fed Mice but Does Not Alleviate Insulin Resistance

The insulin resistance of diet-induced obesity (DIO) is accompanied by inflammation. Previous studies suggest that the anti-inflammatory effects of infliximab, an anti-TNFα chimeric monoclonal antibody, decreases DIO-associated inflammation in mice fed a 60% fat diet. The effectiveness of infliximab at 10 mg/kg Infliximab (IF10) and 100 mg/kg infliximab (IF100) in C57Bl/6J DIO mice was studied in comparison to C57Bl/6J DIO mice administered chimeric IgG (IgG; 10 mg/kg). Treatment consisted of IP injections of infliximab or IgG once per week for 4 weeks. Body weight and fasting arterial glucose was not different in IF10, IF100, and IgG. IF10 and IF100 mice had a decreased presence of crown-like structures in white adipose tissue compared to IgG treated mice. Infliximab resulted in a dose-dependent reduction in macrophage F4/80 staining in white adipose tissue (4.3±0.7% and 1.8±0.2% in IF10 and IF100, respectively) compared to 8.1±1.6% in IgG, validating the anti-inflammatory effect. Insulin action was measured in mice with arterial and venous catheters using the hyperinsulinemic, euglycemic clamp method (insulin dose of 4 mU/kg/min) combined with [3-3H]glucose in conscious, unstressed mice. Glucose infusion rates (GIR) in IgG mice were higher (25±3 mg/kg/min) as compared to IF10 (17±2 mg/kg/min) and IF100 (19±2 mg/kg/min). The greater GIR in IgG as compared to IF10 was due to changes in hepatic endogenous glucose production (suppression of 12±3 mg/kg/min and 5±1 mg/kg/min, respectively) without a difference in glucose utilization. IF100 exhibited small reductions in both hepatic and peripheral insulin action, neither of which reached significance. Mice treated with saline alone were used as an additional control, but neither IF10 nor IF100 had significant effects on insulin action compared to saline controls. In summary, despite profound anti-inflammatory effects of the anti-TNFα drug, Infliximab causes a paradoxically greater hepatic insulin resistance. Disclosure D.A. Roby: None. C. Guan: None. F. James: None. D. Bracy: None. L. Lantier: None. D. Wasserman: None.

Use of Glucose, Glutamine, and Fatty Acids for Trophoblast Respiration in Lean Women, Women With Obesity, and Women With Gestational Diabetes.

Maternal obesity and gestational diabetes mellitus (GDM) are associated with adverse outcomes, particularly with a male fetus. The composition and amount of substrate supplied to the placenta are altered in these conditions. We hypothesized that there are sexually dimorphic differences in utilization of glucose, fatty acids, and glutamine between trophoblast of lean women, women with obesity, and women with GDM. Trophoblasts were isolated from term male or female placentas from lean women, women with obesity, or women with GDM (n = 4 to 6 per group), and syncytiotrophoblast formed during 72 hours before measuring mitochondrial respiration by a fuel flex assay (Seahorse XF96 analyzer). Dependency, capacity, and flexibility for use of glucose, glutamine, and fatty acids were measured with western blot of glucose transporter GLUT1, glutaminase, and carnitine palmitoyltransferase 1A. Sexual dimorphism in syncytiotrophoblast fuel utilization was seen in women with GDM vs lean women with a significant increase in glucose dependency in males and glucose capacity in females, whereas for glutamine, capacity was significantly decreased in males and females but dependency significantly decreased only in females. Fatty acid dependency and capacity significantly increased in male trophoblast and capacity in female trophoblast of women with GDM vs either lean women or women with obesity. In male but not female trophoblast, flexibility to use all three fuels significantly decreased from lean women to women with obesity and women with GDM. In male trophoblast there were significant associations between GLUT1 and glucose dependency (positive) and flexibility (negative). Human syncytiotrophoblast utilizes glutamine for mitochondrial respiration. Utilization of glucose, fatty acids, and glutamine changes in a sexually dimorphic manner with obesity and GDM, predominantly with a male placenta.

Total Antioxidant Capacity; A Potential Biomarker for Non-Invasive Sex Prediction in Culture Medium of Preimplantation Human Embryos.

Objective The presence of a sex related metabolic difference in glucose utilization and, on the other hand, different developmental kinetic rates in human preimplantation embryos, has been previously observed, hawever, the correlation between these two events is unknown. Oxidative stress (OS) induced by higher glucose consumption appears to be a possible cause for the delayed development rate in female embryos. We examined the correlation between glucose consumption and total antioxidant capacity (TAC) concentration in individual embryo culture media for both male and female embryos. Materials and Methods In this cross-sectional study, we evaluated high quality embryos from 51 patients that underwent intracytoplasmic sperm injection (ICSI) and preimplantation genetic diagnosis (PGD) at the Royan Institute between December 2014 and September 2017. The embryos were individually cultured in G-2TMmedium droplets at days 3-5 or 48 hours post PGD. We analysed the spent culture media following embryo transfer for total antioxidant capacity (TAC) and any remaining glucose concentrations through fluorometric measurement by chemiluminecence system which indirectly was used for measurement of glucose consumed by embryos. Results The results showed that female embryos consumed more glucose which was associated with decreased TAC concentration in their culture medium compared to male embryos. The mean of glucose concentration consumed by the female embryos (30.7 ± 4.7 pmol/embryo/hour) was significantly higher than that of the male embryos (25.3 ± 3.3 pmol/embryo/hour) (P<0.001). There were significantly lower levels of TAC in the surrounding culture medium of female embryos (22.60 ± 0.19 nmol/µl) compared with male embryos (24.74 ± 0.27 nmol/µl, P<0.01). ConclusionThis finding highlighted the utilization of sex dependent metabolic diversity between preimplantation embryos for non-invasive sex diagnosis and suggests the TAC concentration as a potential noninvasive biomarker for prediction of sex.

Comparative Metabolomics of Mycoplasma bovis and Mycoplasma gallisepticum Reveals Fundamental Differences in Active Metabolic Pathways and Suggests Novel Gene Annotations.

Mycoplasmas are simple, but successful parasites that have the smallest genome of any free-living cell and are thought to have a highly streamlined cellular metabolism. Here, we have undertaken a detailed metabolomic analysis of two species, Mycoplasma bovis and Mycoplasma gallisepticum, which cause economically important diseases in cattle and poultry, respectively. Untargeted gas chromatography-mass spectrometry and liquid chromatography-mass spectrometry analyses of mycoplasma metabolite extracts revealed significant differences in the steady-state levels of many metabolites in central carbon metabolism, while 13C stable isotope labeling studies revealed marked differences in carbon source utilization. These data were mapped onto in silico metabolic networks predicted from genome wide annotations. The analyses elucidated distinct differences, including a clear difference in glucose utilization, with a marked decrease in glucose uptake and glycolysis in M.bovis compared to M.gallisepticum, which may reflect differing host nutrient availabilities. The 13C-labeling patterns also revealed several functional metabolic pathways that were previously unannotated in these species, allowing us to assign putative enzyme functions to the products of a number of genes of unknown function, especially in M.bovis. This study demonstrates the considerable potential of metabolomic analyses to assist in characterizing significant differences in the metabolism of different bacterial species and in improving genome annotation. IMPORTANCE Mycoplasmas are pathogenic bacteria that cause serious chronic infections in production animals, resulting in considerable losses worldwide, as well as causing disease in humans. These bacteria have extremely reduced genomes and are thought to have limited metabolic flexibility, even though they are highly successful persistent parasites in a diverse number of species. The extent to which different Mycoplasma species are capable of catabolizing host carbon sources and nutrients, or synthesizing essential metabolites, remains poorly defined. We have used advanced metabolomic techniques to identify metabolic pathways that are active in two species of Mycoplasma that infect distinct hosts (poultry and cattle). We show that these species exhibit marked differences in metabolite steady-state levels and carbon source utilization. This information has been used to functionally characterize previously unknown genes in the genomes of these pathogens. These species-specific differences are likely to reflect important differences in host nutrient levels and pathogenic mechanisms.

A 24-Hour Temporal Profile of In Vivo Brain and Heart PET Imaging Reveals a Nocturnal Peak in Brain 18F-Fluorodeoxyglucose Uptake

Using positron emission tomography, we measured in vivo uptake of 18F-fluorodeoxyglucose (FDG) in the brain and heart of C57Bl/6 mice at intervals across a 24-hour light-dark cycle. Our data describe a significant, high amplitude rhythm in FDG uptake throughout the whole brain, peaking at the mid-dark phase of the light-dark cycle, which is the active phase for nocturnal mice. Under these conditions, heart FDG uptake did not vary with time of day, but did show biological variation throughout the 24-hour period for measurements within the same mice. FDG uptake was scanned at different times of day within an individual mouse, and also compared to different times of day between individuals, showing both biological and technical reproducibility of the 24-hour pattern in FDG uptake. Regional analysis of brain FDG uptake revealed especially high amplitude rhythms in the olfactory bulb and cortex, while low amplitude rhythms were observed in the amygdala, brain stem and hypothalamus. Low amplitude 24-hour rhythms in regional FDG uptake may be due to multiple rhythms with different phases in a single brain structure, quenching some of the amplitude. Our data show that the whole brain exhibits significant, high amplitude daily variation in glucose uptake in living mice. Reports applying the 2-deoxy-D[14C]-glucose method for the quantitative determination of the rates of local cerebral glucose utilization indicate only a small number of brain regions exhibiting a day versus night variation in glucose utilization. In contrast, our data show 24-hour patterns in glucose uptake in most of the brain regions examined, including several regions that do not show a difference in glucose utilization. Our data also emphasizes a methodological requirement of controlling for the time of day of scanning FDG uptake in the brain in both clinical and pre-clinical settings, and suggests waveform normalization of FDG measurements at different times of the day.

The presence of the glycolysis operon in SAR11 genomes is positively correlated with ocean productivity

Bacteria in the SAR11 clade are highly abundant in marine surface waters, but currently little is known about the carbon compounds that support these large heterotrophic populations. To better understand the carbon requirements of these organisms, we conducted a multiphasic exploration of carbohydrate utilization among SAR11 isolates from the Northeast Pacific Ocean and the Sargasso Sea. A comparison of three SAR11 genomes showed they all lacked a recognizable PTS system, the oxidative portion of the pentose phosphate shunt (zwf-, pgl-), genes for the Embden-Meyerhoff-Parnas (pfk-, pyk-) and Entner-Doudoroff (eda-) pathways of glycolysis. Strain HTCC7211, isolated from an ocean gyre, was missing other glycolysis genes as well. Growth assays, radioisotopes, metagenomics and microarrays were used to test the hypothesis that these isolates might be limited in their abilities to transport and oxidize exogenous carbohydrates. Galactose, fucose, rhamnose, arabinose, ribose and mannose could not serve as carbon sources for the isolates tested. However, differences in glucose utilization were detected between coastal and ocean gyre isolates, with the coastal isolates capable of transporting, incorporating and oxidizing glucose while the open ocean isolate could not. Subsequent microarray analysis of a coastal isolate suggested that an operon encoding a variant of the Entner-Doudoroff pathway is likely responsible for the observed differences in glucose utilization. Metagenomic analysis indicated this operon is more commonly found in coastal environments and is positively correlated with chlorophyll a concentrations. Our results indicated that glycolysis is a variable metabolic property of SAR11 metabolism and suggest that glycolytic SAR11 are more common in productive marine environments.

Abstract 5105: Increased Glucose Uptake in Visceral versus Subcutaneous Adipose Tissue Revealed by PET Imaging

Background : The amount of visceral and subcutaneous adipose tissue (VAT and SAT, respectively) differentially predicts cardiovascular risk. Beyond volumetric measurement, glucose uptake in adipose tissue might yield additional information for risk stratification. This study explored differences in glucose utilization between VAT and SAT and potential mechanisms for this finding. Methods and Results : Retrospective analysis of whole body FDG-PET scans from 59 patients showed that VAT exhibited higher FDG uptake than SAT (Figure A , p&lt;0.0001) independent of age, gender, body mass index, co-morbidities, or medications. To investigate the mechanisms underlying this observation, we then studied glucose uptake in stromal vascular cells (SVCs), a fraction of the adipose tissue which is rich in inflammatory cells. SVCs from VAT of diet-induced obese C57BL/6 mice exhibited higher glucose uptake than those from SAT (Figure B , n=6, p=0.01). Evaluation of the expression of various genes involved in cellular glucose metabolism such as glucose transporters (GLUT 1, 3 and 4) and hexokinases (HK-1 and 2) showed increased expression of HK-1 in VAT-compared to SAT-derived SVCs (Figure C , n=10, p=0.005). This finding illustrates one mechanism that may explain the above results. Conclusions: This study showed non-invasively with FDG PET imaging that VAT has increased glucose uptake compared to SAT in human subjects, and showed experimentally that inflammatory cells may contribute to this difference. These findings add to our understanding of the nexus between adiposity, inflammation, and cardiovascular risk.

Olfactory bulbectomy reduces cerebral glucose utilization: 2-[ 14C]deoxyglucose autoradiographic study

The olfactory bulbectomized (OBX) rat is an extensively investigated animal model of depression. In the present study the effects of olfactory bulbectomy in drug-naive adult male Sprague–Dawley rats (200–240 g) on global (gCGU) and regional cerebral glucose (rCGU) utilization was evaluated. Two weeks following surgery, the autoradiographic measurement of CGU using [ 14C]-2-deoxyglucose was employed. The levels of CGU in the OBX and sham-operated rats were compared in 40 brain regions. Statistical methods indicate significantly lower levels of global (overall) CGU in the OBX group than in the sham group. Discriminant analysis was done on the z-scores to remove animal to animal variability. The following thirteen regions were identified by the stepwise discriminant analysis of the z-scores as significantly contributing to the differences between the sham and OBX: amygdala, cingulate cortex, caudate putamen at the level of globus pallidus, caudate putamen-lateral part, dorsal subiculum, dorsal thalamus, hypothalamus, median raphe, somatosensory cortex, substantia nigra, ventral hippocampus, ventral tegmental area and the ventral thalamus. The pattern of changes in the rCGU following OBX does not completely correlate with the pattern of connectivity of the olfactory bulbs, however, many regions with direct connection to the olfactory bulbs (e.g., amygdala, hypothalamus, ventral hippocampus, and ventral tegmental area) were found to be important for differentiation. No left to right asymmetries in the rCGU were found. The data suggest that there are very important regional differences in glucose utilization between the OBX and sham operated rats, which points to the need to study antidepressants in an animal model of depression rather than in normal animals.

Different Metabolic Responses in α-, β-, and δ-Cells of the Islet of Langerhans Monitored by Redox Confocal Microscopy

Blood glucose homeostasis is mainly achieved by the coordinated function of pancreatic α-, β-, and δ-cells, which secrete glucagon, insulin, and somatostatin, respectively. Each cell type responds to glucose changes with different secretion patterns. Currently, considerable information can be found about the signal transduction mechanisms that lead to glucose-mediated insulin release in the pancreatic β-cell, mitochondrial activation being an essential step. Increases in glucose stimulate the mitochondrial metabolism, activating the tricarboxylic acid cycle and raising the source of redox electron carrier molecules needed for respiratory ATP synthesis. However, little is known about the glucose-induced mitochondrial response of non- β-cells and its role in the stimulus-secretion coupling process. This limited information is probably a result of the scarcity of these cells in the islet, the lack of identification patterns, and the technical limitations of conventional methods. In this study, we used flavin adenine dinucleotide redox confocal microscopy as a noninvasive technique to specifically monitor mitochondrial redox responses in immunoidentified α-, β-, and δ-cells in freshly isolated intact islets and in dispersed cultured cells. We have shown that glucose provokes metabolic changes in β- and δ-cell populations in a dose-dependent manner. Conversely, no significant responses were observed in α-cells, despite the sensitivity of their metabolism to drugs acting on the mitochondrial function, and their intact ability to develop Ca 2+ signals. Identical results were obtained in islets and in cultures of dispersed cells. Our findings indicate metabolic differences in glucose utilization among the α-, β-, and δ-cell populations, which might be important in the signal transduction events that lead to hormone release.

Effects of low-dose recombinant human insulin-like growth factor-I on insulin sensitivity, growth hormone and glucagon levels in young adults with insulin-dependent diabetes mellitus

Despite recent interest in the therapeutic potential of recombinant human insulin-like growth factor-I (rhIGF-I) in the treatment of diabetes mellitus, its mechanism of action is still not defined. We have studied the effects of low-dose bolus subcutaneous rhIGF-I (40 μg/kg and 20 μg/kg) on insulin sensitivity, growth hormone (GH) and glucagon levels in seven young adults with insulin-dependent diabetes mellitus (IDDM) using a randomized double-blind placebo-controlled crossover study design. Each was subjected to a euglycemic clamp (5 mmol/L) protocol consisting of a variable-rate insulin infusion clamp (6:00 pm to 8:00 am) followed by a two-dose hyperinsulinemic clamp (insulin infusion of 0.75 mU · kg −1 · min −1 from 8 to 10 am and 1.5 mU · kg −1 · min −1 from 10 am to 12 noon) incorporating [6,6 2H 2]glucose tracer for determination of glucose production/utilization rates. Following rhIGF-I administration, the serum IGF-I level (mean ± SEM) increased (40 μg/kg, 655 ± 90 ng/mL, P < .001; 20 μg/kg, 472 ± 67 ng/mL, P < .001; placebo, 258 ± 51 ng/mL). Dose-related reductions in insulin were observed during the period of steady-state euglycemia (1 am to 8 am) (40 μg/kg, 48 ± 5 pmol/L, P = .01; 20 μg/kg, 58 ± 8 pmol/L, P = .03; placebo, 72 ± 8 pmol/L). The mean overnight GH level (40 μg/kg, 9.1 ± 1.4 mU/L, P = .04; 20 μg/kg, 9.6 ± 2.0 mU/L, P = .12; placebo, 11.3 ± 1.7 mU/L) and GH pulse amplitude (40 μg/kg, 18.8 ± 2.9 mU/L, P = .04; 20 μg/kg, 17.0 ± 3.4 mU/L, P > .05; placebo, 23.0 ± 3.7 mU/L) were also reduced. No differences in glucagon, IGF binding protein-1 (IGFBP-1), acetoacetate, or β-hydroxybutyrate levels were found. During the hyperinsulinemic clamp conditions, no differences in glucose utilization were noted, whereas hepatic glucose production was reduced by rhIGF-I 40 μg/kg ( P = .05). Our data demonstrate that in subjects with IDDM, low-dose subcutaneous rhIGF-I leads to a dose-dependent reduction in the insulin level for euglycemia overnight that parallels the decrease in overnight GH levels, but glucagon and IGFBP-1 levels remain unchanged. The decreases in hepatic glucose production during the hyperinsulinemic clamp study observed the following day are likely related to GH suppression, although a direct effect by rhIGF-I cannot be entirely discounted.

Micronized estradiol and progesterone: Effects on carbohydrate metabolism in reproductive-age women

We assessed glucose utilization and insulin sensitivity in normal reproductive-age women after administration of micronized estradiol, micronized progesterone, or the combination of micronized estradiol and progesterone. Hyperglycemic and euglycemic, hyperinsulinemic clamp studies were performed in normal, regularly cycling women both before and after a short course of either micronized estradiol (n = 8), micronized progesterone (n = 8), or micronized estradiol and progesterone (n = 7). All studies were performed after an overnight fast. Glucose and insulin were determined in the control period and then every 2-10 minutes in the hyperglycemic clamp studies and every 5-10 minutes in the euglycemic clamp studies. In the hyperglycemic clamp studies, hyperglycemia was maintained by a variable glucose infusion. In the euglycemic clamp studies, a primed 3-3H glucose infusion (25 microCi) followed by a 0.25-microCi continuous infusion was begun 120 minutes before initiation of the insulin infusion and variable glucose infusion. Samples for glucose radioactivity were measured during the control period and during the last 40 minutes of each step of the euglycemic clamp after establishment of a steady state. No differences in baseline glucose or insulin levels were detected in any of the study groups as compared with control. Glucose utilization as assessed by the hyperglycemic clamp model was not significantly different from control in the estradiol group, the progesterone group, or the group treated with the combination. In all of the treatment groups, no significant differences were noted under euglycemic, hyperinsulinemic conditions in glucose utilization, hepatic glucose production, or insulin sensitivity. Women of reproductive age do not demonstrate significant differences in basal levels of glucose or insulin when given a short course of micronized estradiol and progesterone, either alone or in combination. Under conditions of the hyperglycemic, hyperinsulinemic clamp, the pancreatic beta-cell response to hyperglycemia and glucose utilization is not significantly altered by exogenous administration of hormones. Conditions of the euglycemic, hyperinsulinemic clamp failed to elicit significant differences in glucose utilization and insulin sensitivity in any of the three treatment groups. These findings demonstrate that glucose homeostasis is not altered by the exogenous administration of natural hormones in reproductive-age women.

A prospective, randomized comparison of cerebral venous oxygen saturation during normothermic and hypothermic cardiopulmonary bypass

Recent reports have described cerebral venous oxygen desaturation during and after rewarming from hypothermic cardiopulmonary bypass. Additionally, patients undergoing normothermic cardiopulmonary bypass may be at higher risk for neurologic injury. This study was designed to determine whether patients undergoing normothermic cardiopulmonary bypass are at increased risk for sustained cerebral desaturation. Fifty-two patients undergoing first-time coronary artery bypass grafting were randomized to receive normothermic (37 degrees C, n = 26) or hypothermic (27 degrees C, n = 26) cardiopulmonary bypass. The anesthetic was standardized and alpha-stat pH management was used. A 4F oximetric catheter was placed in the jugular bulb and cerebral venous and radial arterial blood were sampled. Oxygen partial pressure and saturation were measured at six intervals from cerebral venous blood and from radial arterial blood. Patients receiving normothermic cardiopulmonary bypass had lesser values of oxygen partial pressure and saturation in cerebral venous blood than patients subjected to hypothermia during the first 40 minutes of bypass. Cerebral venous desaturation (oxygen saturation in cerebral venous blood of 50% or less) was observed in 54% of patients in the normothermic group and 12% of patients in the hypothermic group during cardiopulmonary bypass. In the normothermic group, cerebral desaturation occurred primarily in early bypass (14 of 26). The three episodes of desaturation in the hypothermic group occurred during rewarming. During cardiopulmonary bypass, the arteriovenous oxygen content difference was greater in the normothermic group than in that in the hypothermic group, suggesting higher oxygen consumption. Differences in glucose utilization during early cardiopulmonary bypass between the groups was also detected. One patient in the hypothermic group had an embolic stroke and subsequently died. There were no other perioperative strokes or deaths in the study population. The present study demonstrates that patients undergoing normothermic cardiopulmonary bypass are at greater risk for cerebral desaturation. Because it is a global assessment, cerebral venous oxygen saturation may be insensitive to focal ischemic events. It remains to be seen whether these differences in cerebral physiologic states translate into differences in clinical outcome.

Adipocyte Insulin Responsiveness in Female Sprague-Dawley Rats Fed a Low Fat Diet Containing a Fat-Mimetic Carbohydrate

Two experiments examined the effects of replacing high fat with low fat diets on adipocyte insulin sensitivity and response. Female Sprague-Dawley rats had free access to diets containing 21% (control), 61% (high fat) or 2% (low fat) of energy as fat. In the low fat diet a carbohydrate-based fat-mimetic carbohydrate replaced all but the essential fat present in the high fat diet. Insulin-stimulated glucose utilization by isolated adipocytes was measured after 10, 30 or 50 d. In a second study adipocyte insulin saturation curves were measured after 36 d. Rats fed the high fat diet for 30 d were insulin resistant and adipocyte basal and insulin-stimulated glucose utilization were depressed. The low fat diet initially stimulated glucose utilization of adipocytes but did not change insulin responsiveness. After 50 d there was no difference in glucose utilization between adipocytes from rats fed control and low fat diets. Insulin resistance in rats fed the high fat diet was associated with a nonsignificant reduction in insulin receptor number. These observations do not exclude the possibility of a post-receptor defect in glucose utilization.

Regional myocardial glucose utilization by developing fetal and maternal hearts

Regional glucose utilization of the developing fetal feline heart was assessed during three stages of gestation and compared with the maternal heart and non-pregnant controls. The specific aims were to determine: 1) if glucose utilization by the whole heart changes from early to late gestation; 2) if there are differences in glucose utilization by specific regions of the heart; 3) if these regional differences in glucose utilization are consistent throughout gestation. Regional myocardial glucose utilization was measured using the [14C] 2-deoxyglucose high spatial resolution autoradiographic technique. Eleven fetal and 16 adult hearts were studied. Two of the fetuses were at 49 days of gestation, three were at 35 days, and six were at 25 days of gestation. This was the first study to assess regional myocardial glucose utilization in the developing fetus. Glucose utilization by the fetal heart was greater than that seen in the normal control adult or maternal heart, and was highest during early gestation. The posterior wall of the left ventricle had glucose utilization twice that measured for the anterior wall. Other regions were not significantly different. This information indicates that availability of glucose to the fetus is important for normal cardiac metabolism and development.