Gymnasium-based unsupervised exercise maintains benefits in oxygen uptake kinetics obtained following supervised training in type 2 diabetes

Supervised exercise (SE) in patients with type 2 diabetes improves oxygen uptake kinetics at the onset of exercise. Maintenance of these improvements, however, has not been examined when supervision is removed. We explored if potential improvements in oxygen uptake kinetics following a 12-week SE that combined aerobic and resistance training were maintained after a subsequent 12-week unsupervised exercise (UE). The involvement of cardiac output (CO) in these improvements was also tested. Nineteen volunteers with type 2 diabetes were recruited. Oxygen uptake kinetics and CO (inert gas rebreathing) responses to constant-load cycling at 50% ventilatory threshold (V_T), 80% V_T, and mid-point between V_T and peak workload (50% Δ) were examined at baseline (on 2 occasions) and following each 12-week training period. Participants decided to exercise at a local gymnasium during the UE. Thirteen subjects completed all the interventions. The time constant of phase 2 of oxygen uptake was significantly faster (p < 0.05) post-SE and post-UE compared with baseline at 50% V_T (17.3 ± 10.7 s and 17.5 ± 5.9 s vs. 29.9 ± 10.7 s), 80% V_T (18.9 ± 4.7 and 20.9 ± 8.4 vs. 34.3 ± 12.7s), and 50% Δ (20.4 ± 8.2 s and 20.2 ± 6.0 s vs. 27.6 ± 3.7 s). SE also induced faster heart rate kinetics at all 3 intensities and a larger increase in CO at 30 s in relation to 240 s at 80% V_T; and these responses were maintained post-UE. Unsupervised exercise maintained benefits in oxygen uptake kinetics obtained during a supervised exercise in subjects with diabetes, and these benefits were associated with a faster dynamic response of heart rate after training.

Regulation of glucose kinetics during intense exercise in humans: effects of α- and β-adrenergic blockade

This study examined the effect of combined α- and β-adrenergic blockade on glucose kinetics during intense exercise. Six endurance-trained men exercised for 20 minutes at approximately 78% of their peak oxygen consumption (V_O 2) following ingestion of a placebo (CON) or combined α- (prazosin hydrochloride) and β- (timolol maleate) adrenoceptor antagonists (BLK). Plasma glucose increased during exercise in CON (0 minutes: 5.5 ± 0.1; 20 minutes: 6.5 ± 0.3 mmol · L⁻¹, P < .05). In BLK, the exercise-induced increase in plasma glucose was abolished (0 minutes: 5.7 ± 0.3; 20 minutes: 5.7 ± 0.1 mmol · L⁻¹). Glucose kinetics were measured using a primed, continuous infusion of [6,6-²H] glucose. Glucose production was not different between trials; on average these values were 25.3 ± 3.9 and 30.9 ± 4.4 μmol · kg⁻¹ · min⁻¹ in CON and BLK, respectively. Glucose uptake during exercise was greater (P < .05) in BLK (30.6 ± 4.6 μmol · kg⁻¹ · min⁻¹) compared with CON (18.4 ± 2.5 μmol · kg⁻¹ · min⁻¹). In BLK, plasma insulin and catecholamines were higher (P < .05), while plasma glucagon was unchanged from CON. Free fatty acids (FFA) and glycerol were lower (P < .05) in BLK. These findings demonstrate that adrenergic blockade during intense exercise results in a blunted plasma glucose response that is due to enhanced glucose uptake, with no significant change in glucose production.

Effect of carbohydrate ingestion on glucose kinetics during exercise in the heat

Six endurance-trained men [peak oxygen uptake (VO₂) = 4.58 ± 0.50 (SE) l/min] completed 60 min of exercise at a workload requiring 68 ± 2% peak VO₂ in an environmental chamber maintained at 35°C (<50% relative humidity) on two occasions, separated by at least 1 wk. Subjects ingested either a 6% glucose solution containing 1 µCi [3-³H]glucose/g glucose (CHO trial) or a sweet placebo (Con trial) during the trials. Rates of hepatic glucose production [HGP = glucose rate of appearance (R_a) in Con trial] and glucose disappearance (R_d), were measured using a primed, continuous infusion of [6,6-^₂H]glucose, corrected for gut-derived glucose (gut R_a) in the CHO trial. No differences in heart rate, VO₂, respiratory exchange ratio, or rectal temperature were observed between trials. Plasma glucose concentrations were similar at rest but increased (P < 0.05) to a greater extent in the CHO trial compared with the Con trial. This was due to the absorption of ingested glucose in the CHO trial, because gut R_a after 30 and 50 min (16 ± 5 µmol · kg^-1 · min^-1) was higher (P < 0.05) compared with rest, whereas HGP during exercise was not different between trials. Glucose R_d was higher (P < 0.05) in the CHO trial after 30 and 50 min (48.0 ± 6.3 vs 34.6 ± 3.8 µmol · kg^-1 · min^-1, CHO vs. Con, respectively). These results indicate that ingestion of carbohydrate, at a rate of ~1.0 g/min, increases glucose Rd but does not blunt the rise in HGP during exercise in the heat.

Slow component of VO2 kinetics: the effect of training status, fibre type, UCP3 mRNA and citrate synthase activity

Examines the relationship between the magnitude of the relative slow component (SC) of pulmonary oxygen uptake VO[sub 2], citrate synthase activity, UCP2 and UCP3 mRNA levels and muscle fiber composition in both endurance-trained and recreationally active subjects. Magnitude of the relative SC of the Tr group; Indicators of aerobic fitness; High negative correlations between the magnitude of the relative SC and citrate synthase activity and VO[sub 2] peak.

Plasma glucose kinetics during prolonged exercise in trained humans when fed carbohydrate

Nine endurance-trained men exercised on a cycle ergometer at ~68% peak O₂ uptake to the point of volitional fatigue [232 ± 14 (SE) min] while ingesting an 8% carbohydrate solution to determine how high glucose disposal could increase under physiological conditions. Plasma glucose kinetics were measured using a primed, continuous infusion of [6,6-²H]glucose and the appearance of ingested glucose, assessed from [3-³H]glucose that had been added to the carbohydrate drink. Plasma glucose was increased (P < 0.05) after 30 min of exercise but thereafter remained at the preexercise level. Glucose appearance rate (Ra) increased throughout exercise, reaching its peak value of 118 ± 7 µmol · kg^-1 · min^-1 at fatigue, whereas gut R_a increased continuously during exercise, peaking at 105 ± 10 µmol · kg^-1 · min^-1 at the point of fatigue. In contrast, liver glucose output never rose above resting levels at any time during exercise. Glucose disposal (R_d) increased throughout exercise, reaching a peak value of 118 ± 7 µmol · kg^-1 · min^-1 at fatigue. If we assume 95% oxidation of glucose R_d, estimated exogenous glucose oxidation at fatigue was 1.36 ± 0.08 g/min. The results of this study demonstrate that glucose uptake increases continuously during prolonged, strenuous exercise when carbohydrate is ingested and does not appear to limit exercise performance.

The effect of vitamin : a deficiency on glucose uptake in the rat

This thesis describes an investigation of the effects of vitamin A deficiency on gut function, The central hypothesis to be tested was that acute vitamin A deficiency affects glucose uptake from the small intestine- The hypothesis was tested using a system involving perfusion of isolated segments of the small intestine in the anaesthetized rat. The system was used to study effects on glucose uptake under steady-state conditions. In the initial part of the study, experiments were diverted towards setting up the system for measuring steady-state uptake, and determining the relative contributions of active uptake and diffusion. Phenol red was found to be a reliable non-absorbable marker for determining net water movement. Phlorizin, generally at 1 mmol/L, was used as a competitive (reversible) inhibitor of active uptake. It is difficult however to confirm complete inhibition of active uptake by phlorizin because of the limited solubility of the inhibitor. The kinetics of glucose uptake f ram intra-luminal maltose were found to be, in general, not significantly different from those applying to the uptake of glucose from an equivalent glucose solution. Maltase activity in the perfused gut segment was found to be sufficient to hydrolyse most of the maltose (80 per cent or more) in the solution being perfused, a much greater proportion than was absorbed. Glucose absorptive capacity, measured on an intestinal dry weight basis, was greatest in the duodenum and progressively less in the jejunum and ileum. The rate of water uptake f ran the gut was increased by the presence of glucose in the lumen, and was linked to glucose uptake as shown by the inhibition of water uptake by phlorizin. Uptake of glucose by solvent drag was demonstrated by showing an increased rate of glucose uptake when the rate of water uptake was increased by perfusing a solution of reduced osmotic pressure. In the experiment a low intra-luminal glucose concentration was used to preclude net uptake by diffusion and active uptake was blocked with phlorizin. This process was further investigated using streptozotocin-diabetic rats in which the diabetes establishes a hyperosomotic blood with hyperglycaemia. Uptake by solvent drag was more obvious in diabetic animals. A back-diffusion (exsorption) of glucose from the tissues to the lumen was also shown; the rate being proportional to plasma glucose concentration. Vitamin A deficiency was established in weanling rats after 6-7 weeks feeding on a diet based on wheat starch, coconut oil, and casein washed with hot ethanol, together with vitamins and minerals. The vitamin A deficiency led to classic eye signs and was reversed by the addition to the diet of retinoic acid (5 g/g diet). Vitamin A deficiency decreased intestinal mucus production (dry weight) but had no detectable effect on the histology of the villous epithelium as shown under the light microscope. Using perfusion experiments it was shown that vitamin A deficiency had no significant effect on the rate of active uptake of glucose, but that deficiency increased the rate of passive uptake.

A non-radioactive method for measuring Cu uptake in HepG2 cells

At present, all data on Cu uptake and metabolism have been derived from radioactive uptake experiments. These experiments are limited by the availability of the radioactive isotopes ⁶⁴Cu or ⁶⁷Cu, and their short half-life (12.5 and 62 h, respectively). In this paper, we investigate an alternative method to study the uptake of Cu with natural isotopes in HepG2 cells, a liver cell line used extensively to study Cu metabolism. In nature, Cu occurs as two stable isotopes, ⁶³Cu and ⁶⁵Cu (⁶³Cu/⁶⁵Cu = 2.23). This ratio can be measured accurately using inductively coupled plasma mass spectrometry (ICP-MS). In initial experiments, we attempted to measure the time course of Cu uptake using ⁶⁵Cu. The change in the ⁶³Cu/⁶⁵Cu ratio, however, was too small to allow measurement of Cu uptake by the cells. To overcome this difficulty, the natural ⁶³Cu/⁶⁵Cu ratio in HepG2 cells was altered using long-term incubation with ⁶³Cu. This had a significant effect on Cu concentration in HepG2 cells, changing it from 81.9 ± 9.46 pmol μg DNA⁻¹ (week 1) to 155 ± 8.63 pmol μg DNA⁻¹ (week 2) and stabilising at 171 ± 4.82 pmol μg DNA⁻¹ (week 3). After three weeks of culture with 2 μM ⁶³Cu the ⁶³Cu/⁶⁵Cu changed from 2.18 ± 0.05 to 15.3 ± 1.01. Cu uptake was then investigated as before using ⁶⁵Cu. Uptake was linear over 60 min, temperature dependent and consistent with previous kinetics data. These observations suggest that stable isotope ICP-MS provides an alternative technique for the study of Cu uptake by HepG2 cells.

Exercise performance and V0₂ kinetics during upright and recumbent high-intensity cycling exercise

This study investigated cycling performance and oxygen uptake (VO₂) kinetics between upright and two commonly used recumbent (R) postures, 65ºR and 30ºR. On three occasions, ten young active males performed three bouts of high-intensity constant-load (85% peak workload achieved during a graded test) cycling in one of the three randomly assigned postures (upright, 65ºR or 30ºR). The first bout was performed to fatigue and second and third bouts were limited to 7 min. A subset of seven subjects performed a final constant-load test to failure in the supine posture. Exercise time to failure was not altered when the body inclination was lowered from the upright (13.1 ± 4.5 min) to 65ºR (10.5 ± 2.7 min) and 30ºR (11.5 ± 4.6 min) postures; but it was significantly shorter in the supine posture (5.8 ± 2.1 min) when compared with the three inclined postures. Resulting kinetic parameters from a tri-exponential analysis of breath-by-breath VO₂ data during the first 7 min of exercise were also not different between the three inclined postures. However, inert gas rebreathing analysis of cardiac output revealed a greater cardiac output and stroke volume in both recumbent postures compared with the upright posture at 30 s into the exercise. These data suggest that increased cardiac function may counteract the reduction of hydrostatic pressure from upright ~25 mmHg; to 65ºR ~22 mmHg; and 30ºR ~18 mmHg such that perfusion of active muscle presumably remains largely unchanged, and also therefore, VO₂ kinetics and performance during high-intensity cycling.

Evaluation of cassava peel waste as lowcost biosorbent for Ni-sorption : equilibrium, kinetics, thermodynamics and mechanism

The feasibility of cassava peel waste for Ni-sorption is evaluated in this work. The biosorbents are characterized by Boehm titration, Fourier transform-infra red (FTIR) spectroscopy, Nitrogen sorption, scanning electron microscopy-energy dispersive X-ray (SEM-EDX) analysis (e.g. elemental mapping) and X-ray photoelectron spectroscopy (XPS). Adsorption experiments are performed in batch mode at 30 °C (303.15 K), 45 °C (318.15 K) and 60 °C (333.15 K). The performance of several temperature dependence forms of isotherm models e.g. Langmuir, Freundlich, Sips and Toth to represent the adsorption equilibrium data is evaluated and contrasted. Sips model demonstrates the best fitting with the maximum uptake capacity for Ni(II) ions of 57 mg/g (0.971 mmol/g) at pH 4.5. For kinetic data correlation, pseudo-second order model shows the best representation. The chemisorption mechanism and thermodynamics aspect are also discussed.

Effect of adrenaline on glucose kinetics during exercise in adrenalectomised humans

1. The role of adrenaline in regulating hepatic glucose production and muscle glucose uptake during exercise was examined in six adrenaline deficient, bilaterally adrenalectomised humans. Six sex and age matched healthy individuals served as controls (CON).

2. Adrenalectomised subjects cycled for 45 min at 68 ± 1% maximum pulmonary Oμ uptake (VOμ,max), followed by 15 min at 84 ± 2% VOμ,max without (−ADR) or with (+ADR) adrenaline infusion, which elevated plasma adrenaline levels (45 min, 4·49 ± 0·69 nmol l¢; 60 min, 12·41 ± 1·80 nmol l¢; means ± s.e.m.). Glucose kinetics were measured using [3_ÅH]glucose.

3. Euglycaemia was maintained during exercise in CON and −ADR, whilst in +ADR plasma glucose was elevated. The exercise induced increase in hepatic glucose production was similar in +ADR and −ADR; however, adrenaline infusion augmented the rise in hepatic glucose production early in exercise. Glucose uptake increased during exercise in +ADR and −ADR, but was lower and metabolic clearance rate was reduced in +ADR.

4. During exercise noradrenaline and glucagon concentrations increased, and insulin and cortisol concentrations decreased, but plasma levels were similar between trials. Adrenaline infusion suppressed growth hormone and elevated plasma free fatty acids, glycerol and lactate. Alanine and â_hydroxybutyrate levels were similar between trials.

5. The results demonstrate that glucose homeostasis was maintained during exercise in adrenalectomised subjects. Adrenaline does not appear to play a major role in matching hepatic glucose production to the increase in glucose clearance. In contrast, adrenaline infusion results in a mismatch by simultaneously enhancing hepatic glucose production and inhibiting glucose clearance.

Effect of increased blood glucose availability on glucose kinetics during exercise

This study examined the effect of increased blood glucose availability on glucose kinetics during exercise. Five trained men cycled for 40 min at 77 ± 1% peak oxygen uptake on two occasions. During the second trial (Glu), glucose was infused at a rate equal to the average hepatic glucose production (HGP) measured during exercise in the control trial (Con). Glucose kinetics were measured by a primed continuous infusion ofd-[3-3H]glucose. Plasma glucose increased during exercise in both trials and was significantly higher in Glu. HGP was similar at rest (Con, 11.4 ± 1.2; Glu, 10.6 ± 0.6 μmol ⋅ kg−1 ⋅ min−1). After 40 min of exercise, HGP reached a peak of 40.2 ± 5.5 μmol ⋅ kg−1 ⋅ min−1in Con; however, in Glu, there was complete inhibition of the increase in HGP during exercise that never rose above the preexercise level. The rate of glucose disappearance was greater (P < 0.05) during the last 15 min of exercise in Glu. These results indicate that an increase in glucose availability inhibits the rise in HGP during exercise, suggesting that metabolic feedback signals can override feed-forward activation of HGP during strenuous exercise.

Effect of heat stress on glucose kinetics during exercise

To identify the mechanism underlying the exaggerated hyperglycemia during exercise in the heat, six trained men were studied during 40 min of cycling exercise at a workload requiring 65% peak pulmonary oxygen uptake (V˙o 2 peak) on two occasions at least 1 wk apart. On one occasion, the ambient temperature was 20°C [control (Con)], whereas on the other, it was 40°C [high temperature (HT)]. Rates of glucose appearance and disappearance were measured by using a primed continuous infusion of [6,6-2H]glucose. No differences in oxygen uptake during exercise were observed between trials. After 40 min of exercise, heart rate, rectal temperature, respiratory exchange ratio, and plasma lactate were all higher in HT compared with Con (P < 0.05). Plasma glucose levels were similar at rest (Con, 4.54 ± 0.19 mmol/l; HT, 4.81 ± 0.19 mmol/l) but increased to a greater extent during exercise in HT (6.96 ± 0.16) compared with Con (5.45 ± 0.18;P < 0.05). This was the result of a higher glucose rate of appearance in HT during the last 30 min of exercise. In contrast, the glucose rate of disappearance and metabolic clearance rate were not different at any time point during exercise. Plasma catecholamines were higher after 10 and 40 min of exercise in HT compared with Con (P < 0.05), whereas plasma glucagon, cortisol, and growth hormone were higher in HT after 40 min. These results indicate that the hyperglycemia observed during exercise in the heat is caused by an increase in liver glucose output without any change in whole body glucose utilization.

Controllable drug uptake and nongenomic response through estrogen-anchored cyclodextrin drug complex

Breast cancer is a leading killer of women worldwide. Cyclodextrin-based estrogen receptor-targeting drug-delivery systems represent a promising direction in cancer therapy but have rarely been investigated. To seek new targeting therapies for membrane estrogen receptor-positive breast cancer, an estrogen-anchored cyclodextrin encapsulating a doxorubicin derivative Ada-DOX (CDE1-Ada-DOX) has been synthesized and evaluated in human breast cancer MCF-7 cells. First, we synthesized estrone-conjugated cyclodextrin (CDE1), which formed the complex CDE1-Ada-DOX via molecular recognition with the derivative adamantane-doxorubicin (Ada-DOX) (Kd =1,617 M(-1)). The structure of the targeting vector CDE1 was fully characterized using (1)H- and (13)C-nuclear magnetic resonance, mass spectrometry, and electron microscopy. CDE1-Ada-DOX showed two-phase drug-release kinetics with much slower release than Ada-DOX. The fluorescence polarization analysis reveals that CDE1-Ada-DOX binds to recombinant human estrogen receptor α fragments with a Kd of 0.027 µM. Competition assay of the drug complex with estrogen ligands demonstrated that estrone and tamoxifen competed with CDE1-Ada-DOX for membrane estrogen receptor binding in MCF-7 cells. Intermolecular self-assembly of CDE1 molecules were observed, showing tail-in-bucket and wire-like structures confirmed by transmission electronic microscopy. CDE1-Ada-DOX had an unexpected lower drug uptake (when the host-guest ratio was >1) than non-targeting drugs in MCF-7 cells due to ensconced ligands in cyclodextrins cavities resulting from the intermolecular self-assembly. The uptake of CDE1-Ada-DOX was significantly increased when the host-guest ratio was adjusted to be less than half at the concentration of CDE1 over 5 µM due to the release of the estrone residues. CDE1 elicited rapid activation of mitogen-activated protein kinases (p44/42 MAPK, Erk1/2) in minutes through phosphorylation of Thr202/Tyr204 in MCF-7 cells. These results demonstrate a targeted therapeutics delivery of CDE1-Ada-DOX to breast cancer cells in a controlled manner and that the drug vector CDE1 can potentially be employed as a molecular tool to differentiate nongenomic from genomic mechanism.