Comparison of T1 relaxation times in adipose tissue of severely obese patients and healthy lean subjects measured by 1.5 T MRI

Subcutaneous (SAT) and visceral adipose tissue (VAT) differ in composition, endocrine function and localization in the body. VAT is considered to play a role in the pathogenesis of insulin resistance, type 2 diabetes, fatty liver disease, and other obesity‐related disorders. It has been shown that the amount, distribution, and (cellular) composition of adipose tissue (AT) correlate well with metabolic conditions. In this study, T₁ relaxation times of AT were measured in severely obese subjects and compared with those of healthy lean controls. Here, we tested the hypothesis that T₁ relaxation times of AT differ between lean and obese individuals, but also between VAT and SAT as well as superficial (sSAT) and deep SAT (dSAT) in the same individual. Twenty severely obese subjects (BMI 41.4 ± 4.8 kg/m²) and ten healthy lean controls matched for age (BMI 21.5 ± 1.9 kg/m²) underwent MRI at 1.5 T using a single‐shot fast spin‐echo sequence (short‐tau inversion recovery) at six different inversion times (T_I range 100–1000 ms). T₁ relaxation times were computed for all subjects by fitting the T_I‐dependent MR signal intensities of user‐defined regions of interest in both SAT and VAT to a model function. T₁ times in sSAT and dSAT were only measured in obese patients. For both obese patients and controls, the T₁ times of SAT (275 ± 14 and 301 ± 12 ms) were significantly (p < 0.01) shorter than the respective values in VAT (294 ± 20 and 360 ± 35 ms). Obese subjects also showed significant (p < 0.01) T₁ differences between sSAT (268 ± 11 ms) and dSAT (281 ± 19 ms). More important, T₁ differences in both SAT and VAT were highly significant (p < 0.001) between obese patients and healthy subjects. The results of our pilot study suggest that T₁ relaxation times differ between severely obese patients and lean controls, and may potentially provide an additional means for the non‐invasive assessment of AT conditions and dysfunction. Copyright © 2014 John Wiley & Sons, Ltd.     

Cardiac response to exercise in normal-weight and obese, Hispanic men and women: implications for exercise prescription

Aim: The effects of obesity on cardiac function during incremental exercise to peak oxygen consumption (VO_2peak) have not been previously described. The purpose of this study was to compare submaximal and maximal cardiac function during exercise in normal‐weight and obese adults. Methods: Normal‐weight (n = 20; means ± SE: age = 21.9 ± 0.5 years; BMI = 21.8 ± 0.4 kg m^?2) and obese (n = 15; means ± SE: age = 25.1 ± 5.2 years; BMI = 34.1 ± 01.0 kg m^?2) participants were assessed for body composition, VO_2peak and cardiac variables (thoracic bioimpedance analysis) at rest and at heart rates (HR) of 110, 130, 150 and 170 beats min^?1 and maximal HR during incremental cycling exercise to exhaustion. Differences between groups were assessed with mixed‐model ancova with repeated measures. Cardiac variables were statistically indexed for body surface area and resting HR. VO₂ and arteriovenous oxygen difference (a‐vO₂) were statistically indexed for fat‐free mass and resting HR. Results: Significant main effects for group indicated obese participants had higher cardiac output (Q) index and stroke volume (SV) index but lower ejection fraction (EF) and a‐vO₂ index during incremental exercise to exhaustion compared with their normal‐weight peers, despite similar submaximal and maximal VO₂ and absolute power outputs (P < 0.05). Conclusions: Our findings suggest that although Q index and SV index were higher in obese, young adults, EF and a‐vO₂ index were significantly lower when compared to matched, normal‐weight adults.     

Combined spiroergometry and 31P–MRS of human calf muscle during high‐intensity exercise

Simultaneous measurements of pulmonary oxygen consumption (VO₂), carbon dioxide exhalation (VCO₂) and phosphorus magnetic resonance spectroscopy (³¹P–MRS) are valuable in physiological studies to evaluate muscle metabolism during specific loads. Therefore, the aim of this study was to adapt a commercially available spirometric device to enable measurements of VO₂ and VCO₂ whilst simultaneously performing ³¹P–MRS at 3 T. Volunteers performed intense plantar flexion of their right calf muscle inside the MR scanner against a pneumatic MR‐compatible pedal ergometer. The use of a non‐magnetic pneumotachograph and extension of the sampling line from 3 m to 5 m to place the spirometric device outside the MR scanner room did not affect adversely the measurements of VO₂ and VCO₂. Response and delay times increased, on average, by at most 0.05 s and 0.79 s, respectively. Overall, we were able to demonstrate a feasible ventilation response (VO₂ = 1.05 ± 0.31 L/min; VCO₂ = 1.11 ± 0.33 L/min) during the exercise of a single calf muscle, as well as a good correlation between local energy metabolism and muscular acidification (τ_{PCr fast} and pH; R² = 0.73, p < 0.005) and global respiration (τ_{PCr fast} and VO₂; R² = 0.55, p = 0.01). This provides improved insights into aerobic and anaerobic energy supply during strong muscular performances.     

Fraction of unsaturated fatty acids in visceral adipose tissue (VAT) is lower in subjects with high total VAT volume – a combined 1H MRS and volumetric MRI study in male subjects

Visceral adipose tissue (VAT) is thought to play an important role in the pathogenesis of obesity and insulin resistance. However, little is known about the composition of VAT with regard to the amount of mono‐ (MUFAs) and polyunsaturated fatty acids (PUFAs) in triglycerides. Volume‐selective MRS was performed in addition to MRI for the quantification of VAT. Analysis comprised proton signals from the vinyl‐H group (H–C = C–H), including protons from MUFA + PUFA, and diallylic‐H, i.e. methylene‐interrupted PUFAs. The methyl (?CH₃) resonance, which is the only peak with a defined number of protons/triglyceride (n = 9), served as reference. Twenty male subjects participated in this prospective study and underwent MRS of VAT on a 3‐T whole‐body unit. Spectra were recorded by a single‐voxel stimulated echo acquisition mode (STEAM) technique (TE/TM/TR = 20/10/4000 ms; volume of interest between 20 × 25 × 20 and 30 × 30 × 20 mm³; 48–80 acquisitions depending on the size of the volume of interest; bandwidth, 1200 Hz). Post‐processing was performed by a Java‐based magnetic resonance user interface (jMRUI; AMARES). The volume of VAT was quantified in a separate session on a 1.5‐T imager a few days prior to the MRS session by T₁‐weighted imaging. The relative amount of VAT was calculated as a percentage of body weight (%VAT). Ratios of vinyl‐H to –CH₃ and diallylic‐H to –CH₃ were calculated. All spectra recorded from VAT were of high quality, enabling reliable quantification of the mentioned resonances. %VAT and vinyl‐H/CH₃ varied over a broad range (2.8–8.3% and 0.45–0.64, respectively). A strong negative correlation between %VAT and vinyl‐H/CH₃ was found (r = ?0.92), whereas diallylic‐H/CH₃ alone was clearly less well correlated with %VAT (r = ?0.21). The composition of VAT shows strong interindividual variations. The greater the total amount of VAT, the less unsaturated the fatty acids. This is a preliminary result in mainly obese male subjects, and it remains to be determined whether this correlation holds for other cohorts of different age, gender and body mass index. Furthermore, changes in VAT composition during weight loss or different forms of diet have yet to be examined. Copyright © 2012 John Wiley & Sons, Ltd.     

Epidermal growth factor and insulin short‐term increase hPepT1‐mediated glycylsarcosine uptake in Caco‐2 cells

Aims: Little is known about the physiological regulation of the human intestinal di/tri‐peptide transporter, hPepT1. In the present study we evaluated the effects of epidermal growth factor (EGF) and insulin on hPepT1‐mediated dipeptide uptake in the intestinal cell line Caco‐2. Methods: Caco‐2 cells were grown on filters for 23–27 days. Apical dipeptide uptake was measured using [¹⁴C]glycylsarcosine([¹⁴C]Gly‐Sar). HPepT1 mRNA levels were investigated using RT‐PCR, cytosolic pH was determined using the pH‐sensitive fluorescent probe BCECF. Results: Basolateral application of EGF increased [¹⁴C]Gly‐Sar uptake with an ED₅₀ value of 0.77 ± 0.25 ng mL^?1 (n = 3?6) and a maximal stimulation of 33 ± 2% (n = 3?6). Insulin stimulated [¹⁴C]Gly‐Sar uptake with an ED₅₀ value of 3.5 ± 2.0 ng mL^?1 (n = 3?6) and a maximal stimulation of approximately 18% (n = 3?6). Gly‐Sar uptake followed simple Michaelis‐Menten kinetics. K_m in control cells was 0.98 ± 0.11 mM (n = 8) and V_max was 1.86 ± 0.07 nmol cm^?2 min^?1 (n = 8). In monolayers treated with 200 ng mL^?1 of EGF, K_m was 1.11 ± 0.05 mM (n = 5) and V_max was 2.79 ± 0.05 nmol cm^?2 min^?1 (n = 5). In monolayers treated with 50 ng mL^?1 insulin, K_m was 1.03 ± 0.08 mM and V_max was 2.19 ± 0.06 nmol cm^?2 min^?1 (n = 5). Kinetic data thus indicates an increase in the number of active transporters, following stimulation. The incrased Gly‐Sar uptake was not accompanied by changes in hPepT1 mRNA, nor by measurable changes in cytosolic pH. Conclusions: Short‐term stimulation with EGF and insulin caused an increase in hPepT1‐mediated uptake of Gly‐Sar in Caco‐2 cell monolayers, which could not be accounted for by changes in hPepT1 mRNA or proton‐motive driving force.     

Temperature Dependence of Free Volume in Pure and Silica‐Filled Poly(dimethyl siloxane) from Positron Lifetime and PVT Experiments

Summary: The microstructure of the free volume and its temperature dependence in two poly(dimethyl siloxane)s (PDMS), one in the pure state and the other filled with 35 wt.‐% of an in situ hydrophobized fumed silica with a specific surface area of 200–300 m² · g^?1, were studied by pressure‐volume‐temperature experiments (PVT, T = 22–156 °C, P = 10–200 MPa) and positron annihilation lifetime spectroscopy (PALS, T = ?173–100 °C, P = 10^?5 MPa). The Simha‐Somcynsky equation of state was used to estimate the hole free volume fraction, h, and free and occupied volumes, V_f = hV and V_occ = (1 ? h)V, from the specific total volume, V. The PALS spectra were analyzed with the routine LT9.0, which allowed for a dispersion, σ_i, in all three of the lifetimes: the para‐positronium (p‐Ps, τ₁), positron (e⁺, τ₂), and ortho‐positronium (o‐Ps) lifetime (τ₃). This kind of analysis delivered correct p‐Ps lifetime parameters, τ₁, σ₁, and I₁. It was speculated that e⁺, like o‐Ps, undergoes Anderson localization at empty sites of the, static or dynamic, disordered structure. The hole size distribution, its mean value, 〈v_h〉, and dispersion, σ_h, were calculated from the o‐Ps lifetimes. A comparison of 〈v_h〉 with V_f was used to estimate the specific hole number, . During melting of the semicrystalline samples at?38 °C (T_m), 〈v_h〉 increased abruptly, and σ_h suddenly decreased. Both effects are explained by the disappearance of the rigid‐amorphous fraction (RAF) and, thus, a reduction in the dynamic heterogeneity. The following leveling‐off in 〈v_h〉 and the low value of σ_h are attributed to the fast segmental relaxation in the PDMS melts which leads to a smearing of the molecule density distribution around a hole during the o‐Ps lifetime.

     

Nitric oxide modulates acetylcholine‐induced vasodilatation in the hepatic arterial vasculature of the dual‐perfused rat liver

The role of nitric oxide in the modulation of hepatic arterial vascular reactivity was investigated in an isolated dual‐perfused rat liver preparation. Twelve male Wistar rats (200–250 g) were anaesthetized with sodium pentobarbitone (60 mg kg^–1 i.p.). The livers were then excised and perfused in vitro through hepatic arterial and portal venous cannulae at constant flow rates. Concentration‐dependent dose–response curves to acetylcholine (10^–8–10^–5 M ), sodium nitroprusside (10^–6–5 × 10^–4 M ), and adenosine triphosphate (ATP) (10^–8–10^–5 M ) in the hepatic artery were constructed after the tone was raised by addition of methoxamine (3 μM L^–1). Acetylcholine‐induced vasodilatation in the hepatic artery was significantly attenuated with inhibition of nitric oxide synthase by using N^G‐nitro‐L ‐arginine methyl ester (30 μM ), E_max=51.7 ± 2.8 vs. 32.5 ± 3.1 mmHg, before vs. after N^G‐nitro‐L ‐arginine methyl ester, respectively. ATP‐induced hepatic arterial vasoconstriction which was significantly enhanced with L ‐NAME, E_max=94.0 ± 9.3 vs. 127.0 ± 8.0 mmHg, before vs. after N^G‐nitro‐L ‐arginine methyl ester, respectively. Sodium nitroprusside‐induced hepatic arterial vasodilatation remained unchanged with N^G‐nitro‐L ‐arginine methyl ester, E_max=57.0 ± 3.4 vs. 57.0 ± 4.1, before vs. after N^G‐nitro‐L ‐arginine methyl ester, respectively. The data from the present study suggest that acetylcholine‐induced vasodilatation in the intrahepatic arterial vasculature of the rat liver is at least, in part, mediated by the release of nitric oxide. In addition, ATP‐induced hepatic arterial vasoconstriction is also modulated by the release of nitric oxide (*P < 0.05, Student’s paired t‐test).     

Temperature and Pressure Dependence of the Free Volume in Polyisobutylene from Positron Lifetime and Pressure‐Volume‐Temperature Experiments

Summary: The microstructure of the free volume and its temperature and pressure dependence in PIB were studied by PVT experiments and PALS. Employing the Simha–Somcynsky equation of state, the hole‐free volume fraction h and the specific free and occupied volumes, V_f = hV and V_occ = (1 ? h)V, respectively, and their expansivity and compressibility were calculated. From the PALS spectra analyzed using the LT9.0 software, the hole size distribution, the mean hole size 〈v_h〉 and mean dispersion σ_h were calculated. From a comparison of 〈v_h〉 with V_f, the hole density was obtained. It was found that PIB shows an unusual thermal expansion with glass‐like transitions at 210 K and 290 K (at 0 MPa). A similar behavior is observed for tan δ. It was found that at 296 K, 〈v_h〉 decreases exponentially from 80 ų at 0.1 MPa to the extremely low value of 10 ų at 1 300 MPa. Starting from a fluctuation approach, the free‐volume fluctuations and the characteristic length scale (ξ) of dynamic heterogeneity of structural relaxation were estimated from σ_h. It was found that ξ increases from ≈1.5 nm to ≈1.9 nm when the temperature decreases from 293 K to the glass transition temperature T_g = 207 K (at 0 MPa) or the pressure increases from 0.1 MPa to 200 MPa (at 296 K).

Fractional free volume and its mean fluctuation in PIB as determined from positron lifetime spectroscopy and PVT experiments analyzed with the Simha‐Somcynsky equation of state.     

Exercise‐induced lipid peroxidation: Implications for deoxyribonucleic acid damage and systemic free radical generation

Exercise‐induced deoxyribonucleic acid (DNA) damage is often associated with an increase in free radicals; however, there is a lack of evidence examining the two in parallel. This study tested the hypothesis that high‐intensity exercise has the ability to produce free radicals that may be capable of causing DNA damage. Twelve apparently healthy male subjects (age: 23 ± 4 years; stature: 181 ± 8 cm; body mass: 80 ± 9 kg; and VO_2max: 49 ± 5 ml/kg/min) performed three 5 min consecutive and incremental stages (40, 70, and 100% of VO_2max) of aerobic exercise with a 15‐min period separating each stage. Blood was drawn after each bout of exercise for the determination of ex vivo free radicals, DNA damage, protein carbonyls, lipid hydroperoxide (LOOH) concentration, and a range of lipid‐soluble antioxidants. Lipid‐derived oxygen‐centered free radicals (hyperfine coupling constants a_Nitrogen = 13.7 Gauss (G) and aβ_Hydrogen = 1.8 G) increased as a result of acute moderate and high‐intensity exercise (P < 0.05), while DNA damage was also increased (P < 0.05). Systemic changes were observed in LOOH and for lipid‐soluble antioxidants throughout exercise (P < 0.05); however, there was no observed change in protein carbonyl concentration (P > 0.05). These findings identify lipid‐derived free radical species as possible contributors to peripheral mononuclear cell DNA damage in the human exercising model. This damage occurs in the presence of lipid oxidation but in the absence of any change to protein carbonyl concentration. The significance of these findings may have relevance in terms of immune function, the aging process, and the pathology of carcinogenesis. Environ. Mol. Mutagen. 52:35–42, 2011. © 2010 Wiley‐Liss, Inc.     

Validation of a fast method for quantification of intra‐abdominal and subcutaneous adipose tissue for large‐scale human studies

Central obesity is the hallmark of a number of non‐inheritable disorders. The advent of imaging techniques such as MRI has allowed for a fast and accurate assessment of body fat content and distribution. However, image analysis continues to be one of the major obstacles to the use of MRI in large‐scale studies. In this study we assess the validity of the recently proposed fat–muscle quantitation system (AMRA^TM Profiler) for the quantification of intra‐abdominal adipose tissue (IAAT) and abdominal subcutaneous adipose tissue (ASAT) from abdominal MR images. Abdominal MR images were acquired from 23 volunteers with a broad range of BMIs and analysed using sliceOmatic, the current gold‐standard, and the AMRA^TM Profiler based on a non‐rigid image registration of a library of segmented atlases. The results show that there was a highly significant correlation between the fat volumes generated by the two analysis methods, (Pearson correlation r = 0.97, p < 0.001), with the AMRA^TM Profiler analysis being significantly faster (~3 min) than the conventional sliceOmatic approach (~40 min). There was also excellent agreement between the methods for the quantification of IAAT (AMRA 4.73 ± 1.99 versus sliceOmatic 4.73 ± 1.75 l, p = 0.97). For the AMRA^TM Profiler analysis, the intra‐observer coefficient of variation was 1.6% for IAAT and 1.1% for ASAT, the inter‐observer coefficient of variation was 1.4% for IAAT and 1.2% for ASAT, the intra‐observer correlation was 0.998 for IAAT and 0.999 for ASAT, and the inter‐observer correlation was 0.999 for both IAAT and ASAT. These results indicate that precise and accurate measures of body fat content and distribution can be obtained in a fast and reliable form by the AMRA^TM Profiler, opening up the possibility of large‐scale human phenotypic studies. Copyright © 2015 John Wiley & Sons, Ltd.     

Middle cerebral artery blood velocity during exercise with β‐1 adrenergic and unilateral stellate ganglion blockade in humans

A reduced ability to increase cardiac output (CO) during exercise limits blood flow by vasoconstriction even in active skeletal muscle. Such a flow limitation may also take place in the brain as an increase in the transcranial Doppler determined middle cerebral artery blood velocity (MCA V_mean) is attenuated during cycling with β‐1 adrenergic blockade and in patients with heart insufficiency. We studied whether sympathetic blockade at the level of the neck (0.1% lidocain; 8 mL; n=8) affects the attenuated exercise – MCA V_mean following cardio‐selective β‐1 adrenergic blockade (0.15 mg kg^?1 metoprolol i.v.) during cycling. Cardiac output determined by indocyanine green dye dilution, heart rate (HR), mean arterial pressure (MAP) and MCA V_mean were obtained during moderate intensity cycling before and after pharmacological intervention. During control cycling the right and left MCA V_mean increased to the same extent (11.4 ± 1.9 vs. 11.1 ± 1.9 cm s^?1). With the pharmacological intervention the exercise CO (10 ± 1 vs. 12 ± 1 L min^?1; n=5), HR (115 ± 4 vs. 134 ± 4 beats min^?1) and ΔMCA V_mean (8.7 ± 2.2 vs. 11.4 ± 1.9 cm s^?1) were reduced, and MAP was increased (100 ± 5 vs. 86 ± 2 mmHg; P < 0.05). However, sympathetic blockade at the level of the neck eliminated the β‐1 blockade induced attenuation in ΔMCA V_mean (10.2 ± 2.5 cm s^?1). These results indicate that a reduced ability to increase CO during exercise limits blood flow to a vital organ like the brain and that this flow limitation is likely to be by way of the sympathetic nervous system.     

Adenosine induces prolonged anti‐β‐adrenergic effects in guinea‐pig papillary muscle

A sustained anti‐β‐adrenergic effect of adenosine has been reported. This study was initiated to investigate this topic and especially elucidate the role of protein kinase C (PKC). Contractile force amplitude and action potential duration at 90% repolarization (APD₉₀) were measured in guinea‐pig papillary muscles before and after 5 min challenge with 5 nm isoproterenol. Protocols contained 30 min exposure to the test agents adenosine 33 μm (ado), adenosine + PKC‐inhibitor bisindolylmaleimide 20 nM (ado + BIM), PKC‐activator 1,2‐dioctanoyl‐sn‐glycerol 10 μm (DOG) and α‐agonist phenylephrine 5 μm (phe). Isoproterenol was given at the end of test exposure and after 15 min washout. Results are mean ± SEM of percentage‐change, P ≤ 0.05 considered significant and labelled *. The first isoproterenol challenge significantly increased contractile force (27 ± 7%*) in the control group. Responses in the test groups were 2 ± 4 (ado), 1 ± 5 (ado + BIM), 14 ± 4* (DOG), 0 ± 2% (phe). After washout of adenosine, DOG and phenylephrine, isoproterenol induced 3 ± 8 (ado), 23 ± 5* (ado + BIM), 13 ± 5* (DOG), 15 ± 7% (phe) increase in test groups compared with 22 ± 5%* increase in contractile force in the control group. After 45 min washout of adenosine the inotropic response was still significantly reduced compared with control (29 ± 4 vs. 79 ± 8%*). Isoproterenol stimulation shortened APD₉₀ in controls at both time points (5 ± 1%* and 4 ± 1%*), with no significant shortening in test groups. Adenosine induces sustained anti‐β‐adrenergic effects on contractile force as well as APD₉₀. A role for PKC in signal transduction is supported with respect to contractile force.     

Reducing plasma free fatty acids by acipimox improves glucose tolerance in high‐fat fed mice

To study whether free fatty acids (FFAs) contribute to glucose intolerance in high‐fat fed mice, the derivative of nicotinic acid, acipimox, which inhibits lipolysis, was administered intraperitoneally (50 mg kg^?1) to C57BL/6J mice which had been on a high‐fat diet for 3 months. Four hours after administration of acipimox, plasma FFA levels were reduced to 0.46 ± 0.06 mmol L^?1 compared with 0.88 ± 0.10 mmol L^?1 in controls (P < 0.001). At this point, the glucose elimination rate after an intravenous glucose load (1 g kg^?1) was markedly improved. Thus, the elimination constant (K_G) for the glucose disposal between 1 and 50 min after the glucose challenge was increased from 0.54 ± 0.01% min^?1 in controls to 0.66 ± 0.01% min^?1 by acipimox (P < 0.001). In contrast, the acute insulin response to glucose (1–5 min) was not significantly different between the groups, although the area under the insulin for the entire 50‐min period after glucose administration was significantly reduced by acipimox from 32.1 ± 2.9 to 23.9 ± 1.2 nmol L^?1 × 50 min (P=0.036). This, however, was mainly because of lower insulin levels at 20 and 50 min because of the lowered glucose levels. In contrast, administration of acipimox to mice fed a normal diet did not affect plasma levels of FFA or the glucose elimination or insulin levels after the glucose load. It is concluded that reducing FFA levels by acipimox in glucose intolerant high‐fat fed mice improves glucose tolerance mainly by improving insulin sensitivity making the ambient islet function adequate, suggesting that increased FFA levels are of pathophysiological importance in this model of glucose intolerance.     

The effects of short recovery duration on <Emphasis Type="Italic">V</Emphasis>O<Subscript>2</Subscript> and muscle deoxygenation during intermittent exercise

This study compared the oxygen uptake (VO₂) and muscle deoxygenation (∆HHb) of two intermittent protocols to responses during continuous constant load cycle exercise in males (24 year ± 2, n = 7). Subjects performed three protocols: (1) 10 s work/5 s active recovery (R), R at 20 W (INT1): (2) 10 s work/5 s R, R at moderate intensity (INT2); and (3) continuous exercise (CONT), all for 10 min, on separate days. The work rate of CONT and the 10 s work of INT1 and INT2 were set within the heavy intensity domain. VO₂ and ∆HHb data were filtered and averaged to 5 s bins. Average VO₂ (80–420 s) was highest during CONT (3.77 L/min), lower in INT2 (3.04 L/min), and lowest during INT1 (2.81 L/min), all (p < 0.05). Average ∆HHb (80–420 s) was higher during CONT (p < 0.05) than both INT exercise protocols (CONT; 25.7 ± 0.9 a.u. INT1; 16.4 ± 0.8 a.u., and INT2; 15.8 ± 0.8 a.u.). The repeated changes in metabolic rate elicited oscillations in ΔHHb in both intermittent protocols, whereas oscillations in VO₂ were only observed during INT1. The greater ΔHHb during CONT suggests a reduction in oxygen delivery compared to oxygen consumption relative to INT. The higher VO₂ for INT 2 versus INT 1 and similar ΔHHb during INT suggests an increase in oxygen delivery during INT 2. Thus the different demands of INT1, INT2, and CONT protocols elicited differing physiological responses to a similar heavy intensity power output. These intermittent exercise models seem to elicit an elevated O₂ delivery condition compared to CONT.     

EPR Investigations into the Kinetics of Trithiocarbonate‐Mediated RAFT‐Polymerization of Butyl Acrylate

Electron paramagnetic resonance (EPR) spectroscopy is used for measuring rate coefficients of addition, k_ad, and fragmentation, k_β, together with the associated equilibrium constants, K_eq, for butyl acrylate polymerizations mediated by S‐ethyl propan‐2‐ylonate‐S’‐propyl trithiocarbonate (EPPT) and by S‐S’‐bis(methyl‐2‐propionate) trithiocarbonate (BMPT). Experiments at ?40 °C yield k_ad = (3.4 ± 0.3) × 10⁶ L mol^?1 s^?1, k_β = (1.4 ± 0.4) × 10² s^?1, and K_eq = (2.6 ± 0.8) × 10⁴ L mol^?1 for EPPT and k_ad = (4.1 ± 0.9) × 10⁶ L mol^?1 s^?1, k_β = (4.5 ± 0.5) × 10¹ s^?1, and K_eq = (8 ± 4) × 10⁴ L mol^?1 for BMPT. The K_eq values are in satisfactory agreement with data from ab initio calculations.

     

Global brain metabolic quantification with whole‐head proton MRS at 3 T

Total N‐acetyl‐aspartate + N‐acetyl‐aspartate–glutamate (NAA), total creatine (Cr) and total choline (Cho) proton MRS (¹H–MRS) signals are often used as surrogate markers in diffuse neurological pathologies, but spatial coverage of this methodology is limited to 1%–65% of the brain. Here we wish to demonstrate that non‐localized, whole‐head (WH) ¹H–MRS captures just the brain's contribution to the Cho and Cr signals, ignoring all other compartments. Towards this end, 27 young healthy adults (18 men, 9 women), 29.9 ± 8.5 years old, were recruited and underwent T₁‐weighted MRI for tissue segmentation, non‐localizing, approximately 3 min WH ¹H–MRS (T_E/T_R/T_I = 5/10 1 /940 ms) and 30 min ¹H–MR spectroscopic imaging (MRSI) (T_E/T_R = 35/2100 ms) in a 360 cm³ volume of interest (VOI) at the brain's center. The VOI absolute NAA, Cr and Cho concentrations, 7.7 ± 0.5, 5.5 ± 0.4 and 1.3 ± 0.2 mM, were all within 10% of the WH: 8.6 ± 1.1, 6.0 ± 1.0 and 1.3 ± 0.2 mM. The mean NAA/Cr and NAA/Cho ratios in the WH were only slightly higher than the “brain‐only” VOI: 1.5 versus 1.4 (7%) and 6.6 versus 5.9 (11%); Cho/Cr were not different. The brain/WH volume ratio was 0.31 ± 0.03 (brain ≈ 30% of WH volume). Air‐tissue susceptibility‐driven local magnetic field changes going from the brain outwards showed sharp gradients of more than 100 Hz/cm (1 ppm/cm), explaining the skull's Cr and Cho signal losses through resonance shifts, line broadening and destructive interference. The similarity of non‐localized WH and localized VOI NAA, Cr and Cho concentrations and their ratios suggests that their signals originate predominantly from the brain. Therefore, the fast, comprehensive WH‐¹H‐MRS method may facilitate quantification of these metabolites, which are common surrogate markers in neurological disorders.     

Exercise and myocardial tolerance to ischaemia‐reperfusion

It is well established that both short‐term (1–5 days) and long‐term (weeks to months) high intensity exercise (i.e. 70–75%VO_2max) provides cardioprotection against ischaemia‐reperfusion injury. However, it is unclear if moderate intensity exercise will also provide cardioprotection. Aim: Therefore, these experiments compared the protective effects of moderate vs. high intensity exercise in providing defense against ischaemia‐reperfusion injury. Methods: Male Sprague–Dawley rats were randomly assigned to one of three‐experimental groups: (1) sedentary (control); (2) moderate intensity treadmill exercise (60 min day^?1 at ～55%VO_2max); or (3) high intensity treadmill exercise (60 min day^?1 at ～75%VO_2max). Hearts were exposed to 20 min of global ischaemia followed by 30 min reperfusion in an isolated working heart preparation. Results: Compared with sedentary rats, both moderate and high intensity exercised rats maintained a higher (P < 0.05) percentage of pre‐ischaemia cardiac output and cardiac work (cardiac output × systolic blood pressure) during reperfusion. No differences in the percent recovery of cardiac output and heart work existed (P > 0.05) between the two exercise groups. Conclusions: These data reveal that both moderate and high intensity exercise training provide equivalent protection against ischaemia‐reperfusion injury.     

The Photo Physical Properties of Dendrimers Containing 1,4‐Dioxo‐3,6‐Diphenylpyrrolo[3,4‐c]pyrrole (DPP) as a Core

Summary: The photophysical properties of dendrimers with 1,4‐dioxo‐3,6‐diphenylpyrrolo[3,4‐c]pyrrole, also known as DPP, as a core were studied. DPP itself has a high quantum yield of fluorescence, as well as a high molar decadic absorption coefficient, ε (ε = 33 000 L · mol^?1 · cm^?1). The dendrimers, which differ by their substitution pattern, either at the nitrogen (DPPN) or at the carbon (DPPC), are studied in various solvents with different viscosity and solvent‐probe interaction and this for several generations and thus varying molecular volume. The stationary measurements show no difference in the absorption and emission spectra for the different generations nor a solvent‐effect. Single photon timing is used to determine the fluorescence lifetime, τ. For both dendrimers, the decay curves can be fitted to a mono‐exponential model. By means of fluorescence depolarization and fluorescence correlation spectroscopy, the hydrodynamic volumes (V_h) are determined. The results for both dendrimers as well as for both techniques are compared. The hydrodynamic radii of DPPN are similar when obtained by FCS compared with anisotropy. When the properties of the different dendrimers are compared, it can be shown that the hydrodynamic volumes of the first generation DPPC dendrimer are much larger compared to V_h of the DPPN dendrimers. The volumes for the third generation are comparable for both substitution patterns.

     

Dopamine‐induced inhibition of Na+‐K+‐ATPase activity requires integrity of actin cytoskeleton in opossum kidney cells

The present study evaluated the importance of the association between Na⁺‐K⁺‐ATPase and the actin cytoskeleton on dopamine‐induced inhibition of Na⁺‐K⁺‐ATPase activity. The approach used measures the transepithelial transport of Na⁺ in monolayers of opossum kidney (OK) cells, when the Na⁺ delivered to Na⁺‐K⁺‐ATPase was increased at the saturating level by amphotericin B. The maximal amphotericin B (1.0 μg mL^–1) induced increase in short‐circuit current (I_sc) was prevented by ouabain (100 μM ) or removal of apical Na⁺. Dopamine (1 μM ) applied from the apical side significantly decreased (29 ± 5% reduction) the amphotericin B‐induced increase in I_sc, this being prevented by the D₁‐like receptor antagonist SKF 83566 (1 μM ) and the protein kinase C (PKC) inhibitor chelerythrine (1 μM ). Exposure of OK cells to cytochalasin B (1 μM ) or cytochalasin D (1 μM ), inhibitors of actin polymerization, from both cell sides reduced by 31 ± 4% and 36 ± 3% the amphotericin B‐induced increase in I_sc and abolished the inhibitory effect of apical dopamine (1 μM ), but not that of the PKC activator phorbol‐12,13‐dibutyrate (PDBu; 100 nM ). Colchicine (1 μM ) failed to alter the inhibitory effects of dopamine. The relationship between Na⁺‐K⁺‐ATPase and the concentration of extracellular Na⁺ showed a Michaelis–Menten constant (K_m) of 44.1 ± 13.7 mM and a V_max of 49.6 ± 4.8 μA cm^–2 in control monolayers. In the presence of apical dopamine (1 μM ) or cytochalasin B (1 μM ) V_max values were significantly (P < 0.05) reduced without changes in K_m values. These results are the first, obtained in live cells, showing that the PKC‐dependent inhibition of Na⁺‐K⁺‐ATPase activity by dopamine requires the integrity of the association between actin cytoskeleton and Na⁺‐K⁺‐ATPase.     

Free Volume,Glass Transition and Degree of Branching in Ethylene/α‐Olefin Copolymers: Positron Lifetime,Differential Scanning Calorimetry,Wide‐Angle X‐Ray Scattering,and Density Studies

Summary: Positron annihilation lifetime spectroscopy, differential scanning calorimetry, wide‐angle X‐ray scattering, and density measurements were used to systematically study the variation of the glass transition temperature T_g and the mean size v_h of holes (local free volumes) in n‐alkyl branched polyethylenes. The samples were commercial ethylene‐rich copolymers with 1‐propene, 1‐butene, and 1‐octene comonomers. From the total specific volume V and the crystallinity X_c the specific volume of the amorphous phase V_a was estimated and used to calculate the specific hole‐free volume V_f. It was found that T_g and X_c decrease and V, V_a, V_f, and v_h increase with increasing weight fraction of comonomers. Both the real crystalline and amorphous specific volumes decrease with increasing crystallinity X_c. For not too high contents of comonomers, T_g decreases and v_h increases linearly with the number and with the length of n‐alkyl branches. This behavior was attributed to an increased segmental mobility caused by branching. Both T_g and v_h follow linear master curves as a function of the degree of branching if this is defined as the fractional number of carbon atoms in the side chains compared with the total number of carbon atoms. A method for estimating T_g from v_h measured at room temperature is shown. The number density of holes N_h shows a slight variation from 0.6 to 0.8 (±0.1) nm^?3 with increasing branching.