The Precious Few Grams of Glucose During Exercise

As exercise intensity exceeds 65% of maximal oxygen uptake carbohydrate energy sources predominate. However, relative to the meager 4–5 g blood glucose pool size in a postabsorptive individual (0.9–1.0 g·L−1 × 5 L blood = 18–20 kcal), carbohydrate (CHO) oxidation rates of 20 kcal·min−1 can be sustained in a healthy and fit person for one hour, if not longer, all the while euglycemia is maintained. While glucose rate of appearance (i.e., production, Ra) from splanchnic sources in a postabsorptive person can rise 2–3 fold during exercise, working muscle and adipose tissue glucose uptake must be restricted while other energy substrates such as glycogen, lactate, and fatty acids are mobilized and utilized. If not for the use of alternative energy substrates hypoglycemia would occur in less than a minute during hard exercise because blood glucose disposal rate (Rd) could easily exceed glucose production (Ra) from hepatic glycogenolysis and gluconeogenesis. The goal of this paper is to present and discuss the integration of physiological, neuroendocrine, circulatory, and biochemical mechanisms necessary for maintenance of euglycemia during sustained hard physical exercise.

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Effects of maternal undernutrition and exercise on glucose kinetics in fetal sheep

British Journal Of Nutrition ◽

10.1079/bjn19900046 ◽

1990 ◽

Vol 64 (2) ◽

pp. 463-472 ◽

Cited By ~ 8

Author(s):

B. J. Leury ◽

K. D. Chandler ◽

A. R. Bird ◽

A. W. Bell

Keyword(s):

Glucose Production ◽

Endogenous Glucose Production ◽

Glucose Disposal ◽

Utilization Rate ◽

Glucose Kinetics ◽

Arterial Blood ◽

Net Uptake ◽

Endogenous Glucose ◽

Total Glucose ◽

Glucose Disposal Rate

Fetal glucose kinetics were measured using a combination of isotope-dilution and Fick-principle methodology in single-pregnant ewes which were either well-fed throughout, or fed at 0.3–0.4 predicted energy requirement for 7–21 d during late pregnancy. All ewes were studied while standing at rest and then while walking on a treadmill at 0.7 m/s on a 10° slope for 60 min. Underfed ewes suffered major decreases in fetal total disposal rate, fetal-placental transfer and umbilical net uptake of glucose, each of which were significantly related to declines in maternal and fetal blood glucose concentrations respectively. In well-fed ewes, fetal endogenous glucose production was negligible, as indicated by the similarity between fetal utilization rate (total glucose disposal rate minus placental uptake of fetal glucose) and umbilical net uptake of glucose, and by nearly identical fetal and maternal arterial blood specific radioactivities of maternally infused D-[2-3H]glucose. By contrast, in underfed ewes, fetal utilization rate greatly exceeded umbilical net uptake of glucose, and the fetal:maternal [3H]glucose specific activity ratio declined significantly, suggesting induction of a substantial rate of fetal endogenous glucogenesis. Exercise caused increases in fetal total glucose disposal rate and glycaemia in fed and underfed ewes. In underfed ewes only, this was accompanied by increased placental uptake of fetal glucose and umbilical net glucose uptake, unchanged fetal glucose utilization and decreased fetal endogenous glucose production. It is concluded that fetal gluconeogenesis makes a major contribution to fetal glucose requirements in undernourished ewes. Increased maternal supply of fetal glucose during exercise substitutes for rather than adds to fetal endogenous glucogenesis.

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Hyperglycemia stimulates carbohydrate oxidation in humans

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.1987.253.4.e376 ◽

1987 ◽

Vol 253 (4) ◽

pp. E376-E382 ◽

Cited By ~ 2

Author(s):

H. Yki-Jarvinen ◽

C. Bogardus ◽

B. V. Howard

Keyword(s):

Fatty Acids ◽

Lipid Oxidation ◽

Substrate Oxidation ◽

Carbohydrate Oxidation ◽

Glucose Disposal ◽

Absolute Rate ◽

Total Rate ◽

Oxidation Rates ◽

Total Glucose ◽

Glucose Availability

We examined whether hyperglycemia stimulates carbohydrate oxidation independent of insulin. Rates of total glucose disposal and substrate oxidation (indirect calorimetry) were measured at 4 insulin concentrations and at each level of insulin at 4 glucose concentrations in 88 separate studies in 22 normal volunteers. The insulin sensitivity of carbohydrate and lipid oxidation was independent of glycemia, but glucose, independent of insulin, increased the absolute rate of carbohydrate oxidation and decreased lipid oxidation. To compare the ability of glucose and insulin to stimulate carbohydrate oxidation, oxidation rates were examined at similar rates of total glucose disposal induced by hyperinsulinemia or hyperglycemia. At physiological matched rates of glucose disposal, insulin stimulated carbohydrate oxidation 2.4-fold more than glucose. The free fatty acids (FFA) were significantly lower in the presence of hyperinsulinemia than hyperglycemia. When compared at similar (supraphysiological) rates of total glucose disposal, where the FFA were completely suppressed, the rate of carbohydrate oxidation was related to the total rate of glucose disposal rather than the ambient glucose or insulin concentrations. We conclude that both glucose and insulin can increase carbohydrate oxidation in humans. We propose that the rate of carbohydrate oxidation is determined by FFA availability and by glucose availability independent of the FFA level in glucose-consuming tissues. Although FFA availability is almost solely determined by insulin, both glucose and insulin can increase carbohydrate oxidation by increasing glucose availability.

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Fatty acids oxidation and alternative energy sources detected in Taenia crassiceps cysticerci after host treatment with antihelminthic drugs

Experimental Parasitology ◽

10.1016/j.exppara.2012.03.017 ◽

2012 ◽

Vol 131 (1) ◽

pp. 111-115 ◽

Cited By ~ 10

Author(s):

Carolina Miguel Fraga ◽

Tatiane Luiza Costa ◽

José Clecildo Barreto Bezerra ◽

Ruy de Souza Lino Junior ◽

Marina Clare Vinaud

Keyword(s):

Fatty Acids ◽

Alternative Energy ◽

Energy Sources ◽

Taenia Crassiceps ◽

Alternative Energy Sources

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Insulin Sensitivity in Post-Obese Women

Clinical Science ◽

10.1042/cs0870407 ◽

1994 ◽

Vol 87 (4) ◽

pp. 407-413 ◽

Cited By ~ 14

Author(s):

Søren Toubro ◽

Philip Western ◽

Jens Bülow ◽

Ian Macdonald ◽

Anne Raben ◽

...

Keyword(s):

Fatty Acids ◽

Insulin Sensitivity ◽

Lipid Oxidation ◽

Free Fatty Acids ◽

Plasma Concentrations ◽

Glucose Disposal ◽

Obese Women ◽

Basal Plasma ◽

Obese Subjects ◽

Glucose Disposal Rate

1. Both increased and decreased sensitivity to insulin has been proposed to precede the development of obesity. Therefore, insulin sensitivity was measured during a 2 h hyperinsulinaemia (100 m-units min−1 m−2) euglycaemic (4.5 mmol/l) glucose clamp combined with indirect calorimetry in nine weight-stable post-obese women and in nine matched control women preceded by 12 h fasting after 48 h on a standardized diet. 2. Both glucose disposal rate (post-obese women, 9.5 ± 2.2 mg min−1 kg−1, control women, 11.2 ± 1.4 mg min−1 kg−1, not significant) and glucose oxidation (3.6 ± 0.5 mg min−1 kg−1 versus 4.0 ± 0.7 mg min−1 kg−1, not significant) were similar in the two groups during the last 30 min of the clamp. Lipid oxidation also decreased similarly during the clamp in the post-obese women (from 30.4 ± 12 to 2.0 ± 7 J min−1 kg−1) and in the control women (from 33.6 ± 11 to 5.4 ± 8 J min−1 kg−1, not significant). Basal plasma concentrations of free fatty acids were similar, but at the end of the clamp free fatty acids were lower in the post-obese women than in the control women (139 ± 19 and 276 ± 48 μmol/l, P = 0.02). 3. We conclude that the insulin sensitivity of glucose metabolism is unaltered in the post-obese state. The study, however, points to an increased antilipolytic insulin action in post-obese subjects, which may favour fat storage and lower lipid oxidation rate post-prandially. The results suggest that alterations in lipid metabolism may contribute to the explanation of the propensity to obesity in susceptible individuals.

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Regulation of Postabsorptive and Postprandial Glucose Metabolism by Insulin-Dependent and Insulin-Independent Mechanisms: An Integrative Approach

Nutrients ◽

10.3390/nu13010159 ◽

2021 ◽

Vol 13 (1) ◽

pp. 159

Author(s):

George D. Dimitriadis ◽

Eirini Maratou ◽

Aikaterini Kountouri ◽

Mary Board ◽

Vaia Lambadiari

Keyword(s):

Skeletal Muscle ◽

Blood Glucose ◽

Glucose Homeostasis ◽

Glucose Production ◽

Postprandial Glucose ◽

Mass Action ◽

Glucose Disposal ◽

Nonesterified Fatty Acids ◽

Glucose Levels ◽

Blood Glucose Levels

Glucose levels in blood must be constantly maintained within a tight physiological range to sustain anabolism. Insulin regulates glucose homeostasis via its effects on glucose production from the liver and kidneys and glucose disposal in peripheral tissues (mainly skeletal muscle). Blood levels of glucose are regulated simultaneously by insulin-mediated rates of glucose production from the liver (and kidneys) and removal from muscle; adipose tissue is a key partner in this scenario, providing nonesterified fatty acids (NEFA) as an alternative fuel for skeletal muscle and liver when blood glucose levels are depleted. During sleep at night, the gradual development of insulin resistance, due to growth hormone and cortisol surges, ensures that blood glucose levels will be maintained within normal levels by: (a) switching from glucose to NEFA oxidation in muscle; (b) modulating glucose production from the liver/kidneys. After meals, several mechanisms (sequence/composition of meals, gastric emptying/intestinal glucose absorption, gastrointestinal hormones, hyperglycemia mass action effects, insulin/glucagon secretion/action, de novo lipogenesis and glucose disposal) operate in concert for optimal regulation of postprandial glucose fluctuations. The contribution of the liver in postprandial glucose homeostasis is critical. The liver is preferentially used to dispose over 50% of the ingested glucose and restrict the acute increases of glucose and insulin in the bloodstream after meals, thus protecting the circulation and tissues from the adverse effects of marked hyperglycemia and hyperinsulinemia.

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The metabolism of glucose, acetate, palmitate, stearate and oleate in pigs

British Journal Of Nutrition ◽

10.1079/bjn19700072 ◽

1970 ◽

Vol 24 (3) ◽

pp. 705-716 ◽

Cited By ~ 24

Author(s):

C. P. Freeman ◽

D. E. Noakes ◽

E. F. Annison

Keyword(s):

Fatty Acids ◽

Fatty Acid ◽

Blood Glucose ◽

Alimentary Tract ◽

Glucose Production ◽

Acetate Production ◽

Simultaneous Reduction ◽

Mean Values ◽

Blood Glucose Concentrations ◽

Oxidation Of Glucose

1. Isotope dilution techniques were used to measure the rates of entry and oxidation of glucose, acetate, palmitate, stearate and oleate in fed and fasted (16 h) pigs.2. Glucose entry rates measured in eight fed and five fasted (16 h) pigs were 20.6 and 8.0 mg/min per kg0.75 (mean values) respectively. The entry rates in fed pigs were lower than the calculated rates of glucose uptake from the alimentary tract, and the validity of glucose entry rates determined under these conditions is discussed.3. Acetate entry rates were unrelated to the fibre content of the diet, and acetate produced from endogenous metabolism was the main contributor to total acetate production.4. Increased rates of entry and oxidation of palmitate, stearate and oleate were observed in fasted pigs.5. Glucose production in fasted pigs was inhibited by raising the concentration of blood glucose. Infusion of insulin in the fed pig caused a decrease in glucose production and a simultaneous reduction in the mobilization of free fatty acids. When blood glucose concentrations fell below about 55 mg/100 ml the release of free fatty acid into the circulation was restored.

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Ciliary Neurotrophic Factor Prevents Acute Lipid-Induced Insulin Resistance by Attenuating Ceramide Accumulation and Phosphorylation of c-Jun N-Terminal Kinase in Peripheral Tissues

Endocrinology ◽

10.1210/en.2005-1074 ◽

2006 ◽

Vol 147 (5) ◽

pp. 2077-2085 ◽

Cited By ~ 63

Author(s):

Matthew J. Watt ◽

Andrea Hevener ◽

Graeme I. Lancaster ◽

Mark A. Febbraio

Keyword(s):

Insulin Resistance ◽

Skeletal Muscle ◽

Insulin Sensitivity ◽

Hepatic Glucose Production ◽

Glucose Production ◽

Ciliary Neurotrophic Factor ◽

Glucose Disposal ◽

Hepatic Glucose ◽

Ceramide Accumulation ◽

Glucose Disposal Rate

Ciliary neurotrophic factor (CNTF) is a member of the gp130 receptor cytokine family recently identified as an antiobesity agent in rodents and humans by mechanisms that remain unclear. We investigated the impact of acute CNTF treatment on insulin action in the presence of lipid oversupply. To avoid confounding effects of long-term high-fat feeding or genetic manipulation on whole-body insulin sensitivity, we performed a 2-h Intralipid infusion (20% heparinized Intralipid) with or without recombinant CNTF pretreatment (Axokine 0.3 mg/kg), followed by a 2-h hyperinsulinemic-euglycemic clamp (12 mU/kg·min) in fasted, male Wistar rats. Acute Intralipid infusion increased plasma free fatty acid levels from 1.0 ± 0.1 to 2.5 ± 0.3 mm, which subsequently caused reductions in skeletal muscle (insulin-stimulated glucose disposal rate) and liver (hepatic glucose production) insulin sensitivity by 30 and 45%, respectively. CNTF pretreatment completely prevented the lipid-mediated reduction in insulin-stimulated glucose disposal rate and the blunted suppression of hepatic glucose production by insulin. Although lipid infusion increased triacylglycerol and ceramide accumulation and phosphorylation of mixed linage kinase 3 and c-Jun N-terminal kinase 1 in skeletal muscle, CNTF pretreatment prevented these lipid-induced effects. Alterations in hepatic and muscle insulin signal transduction as well as phosphorylation of c-Jun N-terminal kinase 1/2 paralleled alterations in insulin sensitivity. These data support the use of CNTF as a potential therapeutic means to combat lipid-induced insulin resistance.

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Catalyst and Elemental Analysis Involving Biodiesel from Various Feedstocks

Catalysts ◽

10.3390/catal11080971 ◽

2021 ◽

Vol 11 (8) ◽

pp. 971

Author(s):

Ines Simbi ◽

Uyiosa Osagie Aigbe ◽

Oluwaseun Oyekola ◽

Otolorin Adelaja Osibote

Keyword(s):

Fatty Acids ◽

Free Fatty Acids ◽

Alternative Energy ◽

Oxidation Stability ◽

Textural Properties ◽

Bifunctional Catalyst ◽

Energy Sources ◽

Biodiesel Fuel ◽

Fuel Quality ◽

Elemental Contents

The world is currently faced with the depletion of fossil fuel energy sources and their use is associated with environmental pollution. This has triggered the need to seek alternative energy sources that are renewable, sustainable and environmentally benign. Biodiesel, an alternative fuel of interest, is obtainable from biomass feedstocks. In existing biodiesel fuel, there are concerns that it is a contaminant due to its elemental contents, which over time also affect its quality. This study aimed to investigate the influence of a bifunctional catalyst on the conversion of free fatty acids and the elemental composition of biodiesel obtained from waste oils of sunflower and palm feedstocks. The synthesised catalyst was characterised using BET, XRD, FTIR and SEM while ICP-OES and Rancimat were used for elemental contents and oxidation in feedstocks and biodiesels. The effect of Cu, Zn and Fe metals on the stability of synthesised biodiesel was further studied. The catalyst showed characteristics of bifunctionality with improved textural properties necessary for the conversion of high free fatty acids feedstocks to biodiesel, despite increasing Ca content within the produced biodiesel. Sunflower biodiesel showed superior fuel quality, although palm biodiesel had more oxidation stability. An increase in the concentration of metals decreased the induction period, with Cu and Fe being more effective than Zn metal.

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