Tissue Metabolic Rate Research Articles

Nonlinear extension of a hemodynamic linear model for coherent hemodynamics spectroscopy

In this work, we are proposing an extension of a recent hemodynamic model (Fantini, 2014a), which was developed within the framework of a novel approach to the study of tissue hemodynamics, named coherent hemodynamics spectroscopy (CHS). The previous hemodynamic model, from a signal processing viewpoint, treats the tissue microvasculature as a linear time-invariant system, and considers changes of blood volume, capillary blood flow velocity and the rate of oxygen diffusion as inputs, and the changes of oxy-, deoxy-, and total hemoglobin concentrations (measured in near infrared spectroscopy) as outputs. The model has been used also as a forward solver in an inversion procedure to retrieve quantitative parameters that assess physiological and biological processes such as microcirculation, cerebral autoregulation, tissue metabolic rate of oxygen, and oxygen extraction fraction. Within the assumption of “small” capillary blood flow velocity oscillations the model showed that the capillary and venous compartments “respond” to this input as low pass filters, characterized by two distinct impulse response functions. In this work, we do not make the assumption of “small” perturbations of capillary blood flow velocity by solving without approximations the partial differential equation that governs the spatio-temporal behavior of hemoglobin saturation in capillary and venous blood. Preliminary comparison between the linear time-invariant model and the extended model (here identified as nonlinear model) are shown for the relevant parameters measured in CHS as a function of the oscillation frequency (CHS spectra). We have found that for capillary blood flow velocity oscillations with amplitudes up to 10% of the baseline value (which reflect typical scenarios in CHS), the discrepancies between CHS spectra obtained with the linear and nonlinear models are negligible. For larger oscillations (~50%) the linear and nonlinear models yield CHS spectra with differences within typical experimental errors, but further investigation is needed to assess the effect of these differences. Flow oscillations larger than 10–20% are not typically induced in CHS; therefore, the results presented in this work indicate that a linear hemodynamic model, combined with a method to elicit controlled hemodynamic oscillations (as done for CHS), is appropriate for the quantitative assessment of cerebral microcirculation.

Age and sex-related changes in superoxide dismutase activity in bovine tissues

The influence of age, gender, and type of tissue on superoxide dismutase (SOD) activity in bovine organs and tissues was investigated. The investigated material consisted of fragments of tissues and organs (liver, heart, lung, kidney, skeletal muscles, and diaphragm) from healthy cows (n = 15), bulls (n = 15), and female calves (n = 12) collected immediately after slaughter at the slaughterhouse. The total SOD activity was measured in tissue and organ homogenates by spectrophotometric method. PAGE electrophoresis and Western blotting technique with specific anti-SOD antibodies as well as zymography confirmed the presence of enzymatic protein and SOD isoenzymes in examined tissues. The study revealed significant differences in SOD activity between organs and tissues, which might be connected with different metabolic rate. Age-related changes were also observed. SOD activity was twice higher in kidneys, lungs, heart of calves compared to other groups of animals. It was also noticed that SOD activity was higher in younger animals and decreased with ageing among the group of bulls. Gender-related differences were observed in lungs and diaphragm. It was concluded that SOD activity depends on sex steroids, which is reflected in age and gender discrepancies, as well as metabolic rate of tissues.

The thermodynamic brain.

Apart from its complex functionality, the brain is a robust thermodynamic machine; the tissue metabolic rate is high and it is thermally shielded by a skull. Therefore, if there is no high-volume blood flow to cool and stabilize the brain temperature, the possibility of unstable behavior seems to be high. Inflowing arterial blood is normally cooler than the brain tissue temperature, and outflowing venous blood is normally warmer than arterial blood but cooler than the brain tissue. Brain blood flow can thus be understood as a cooler for the brain. Pros and cons of clinical measurement, with clear indication for a multimodal monitoring approach, are discussed along with a brief review of basic facts known about temperature, cerebral blood flow and volume, intracranial pressure, and compartmental compliances of the brain.

Metabolic health benefits of long-chain omega-3 polyunsaturated fatty acids.

Restricting energy intake and increasing physical activity are advocated for reducing obesity, but many individuals have difficulty complying with these recommendations. Consumption of long-chain omega-3 polyunsaturated fatty acids (n-3 LCPUFA) offers multiple mechanisms to counteract obesity, including appetite suppression; circulatory improvements, which promote nutrient delivery to skeletal muscle and changes in gene expression, which shift metabolism toward increased fat oxidation; increased energy expenditure; and reduced fat deposition. n-3 LCPUFA may also alter gene expression in skeletal muscle to suppress catabolic pathways and upregulate anabolic pathways, resulting in greater lean tissue mass, metabolic rate, and maintenance of physical function. n-3 LCPUFA supplementation has been shown to counteract obesity in rodents, but evidence in humans is limited. Epidemiological associations between n-3 LCPUFA intakes and obesity are inconclusive. Several studies, on the other hand, indicate inverse relationships between biomarkers of n-3 LCPUFA status and obesity, although causality is uncertain. There have been few human intervention trials of omega-3 supplementation for obesity; some have indicated potential benefits, especially when combined with energy-restricted diets or exercise. More trials are needed to confirm these effects and identify mechanisms of action.

The intraspecies relationship between tissue turnover and metabolic rate in rats

AbstractEcologists interested in studying fluctuating relationships between consumers and nutrient sources are increasingly involved in modeling the rate at which consumers incorporate dietary components. In mammals a correlation between resting metabolic rate (RMR) and tissue turnover may exist across a range of species. Less is known about the variation of tissue turnover rate within a species, and how that correlates with RMR. Here we examine two strains of rats (Rattus norvegicus) with different RMR to test whether variation in RMR is positively correlated with tissue turnover rate within a species. If RMR, a relatively simple measurement, can be correlated with tissue turnover, then this relationship could be used to better interpret ecological functions, including impact of migratory or seasonally available nutrient sources. Here, the changing isotope signature in rat whole blood was modeled using a modified exponential decay equation and a reaction progress variable model. The modeled rate of turnover, metabolic rate (O2 consumed), and mass were then compared between strains of rats. The mass and RMRs (conditions during which RMRs were determined modified from the ideal, as outlined in the Methods) were significantly different between strains, but half‐life and the metabolic tissue replacement component of turnover (as opposed to turnover from mass gain) were not. No significant correlation was found between RMR and metabolic tissue replacement between the strains. Results suggest that within a species showing a range of RMRs, blood tissue turnover should not vary significantly.

The Significance of Incidental 18F-FDG Uptake in PET/CT at the Gastroesophageal Junction in Predicting Benign and Malignant Disease

Purpose: Positron emission tomography (PET), using the positron-emitting glucose analogue 18F-FDG, relies on the observation that neoplasms metabolize glucose at a higher rate than normal tissues. The rate or intensity of tissue metabolism can be assessed by semi quantitative metrics such as standardized uptake value, or SUV. The goal of this study is to correlate esophageal 18F-FDG uptake by PET with esophageal disease identified endoscopically to identify functional imaging factors that might distinguish benign and malignant esophageal disorders. Methods: We reviewed medical records for the period June, 2009 through May, 2012 to identify patients who had both a PET/CT scan and an endoscopy (EGD) performed within six months of one another. Metabolic activity was quantified utilizing volumetric SUV max and SUV mean at the gastro-esophageal junction (GEJ) for all patients. PET characteristics were correlated with EGD findings at the GEJ. Results: From an initial cohort of 285, we identified 220 patients who had both PET/CT and EGD performed within a six months. Patients were grouped into the following categories based on EGD results: esophageal malignancy (n=34), esophagitis (n=21), Barrett's esophagus (n=8), other non-malignant disorders (n=5) and normal (n=151). The average SUV max values for esophageal malignancy, esophagitis, Barrett's esophagus, other and normal were 6.72, 2.47, 2.40, 3.48 and 2.06, respectively. SUV measurements differed significantly between patients with malignancy and normal (p<0.001); these values also differed significantly between patients with malignancy compared to those with Barrett's and esophagitis (p<0.001). There was no significant difference in SUV max that would allow differentiation of normal EGD findings from any individual benign esophageal disorder; however, there was a significant difference in SUV mean comparing normal to the total group of 34 patients with proven benign esophageal disorders (p<0.04). Conclusion: The current study establishes PET SUV values which may be useful in distinguishing patients with concern for esophageal malignancy, benign disorders, or normal findings. Clinicians might find these results useful in determining the need for EGD in patients with unexpectedly high PET 18F-FDG uptake at the gastro-esophageal junction.

Advances in the understanding of specific metabolic rates of major organs and tissues in humans

To present recent evidence on organ and tissue metabolic rates in humans to explain the variance in resting energy expenditure (REE). In humans, present knowledge on specific metabolic activities (i.e. ki-values) refers to seven organs and tissues - brain, heart, liver, kidneys, skeletal muscle, adipose tissue and residual mass - with ki-values of 240, 440, 200, 440, 13, 4.5 and 12 kcal/kg/day, provided by Elia in 1992. Detailed body composition data, as derived from whole body MRI together with measurements of whole body REE, were used to validate ki-values in nonobese, healthy and middle-aged adults. There is no sex difference, but minor, that is 2 and 3% deviations are found for age above 55 years and obesity, respectively. By contrast, in adolescents, differences of about 100 kcal/day or 7.3% of measured REE were observed. There is first evidence for changes in ki-values with either weight loss or weight regain after weight loss. Altogether these data suggest that in adolescence and at age above 55 years, in the obese and with weight change, organ and tissue masses differ in cellularity and/or their specific metabolic rates. Presently, direct assessment of specific organ and tissue metabolic rates in humans by either NMR spectroscopy or PET, together with detailed body composition analysis, has not been performed systematically. We need to become more skilled in methods and models used for detailed body composition analysis together with detailed assessment of energy expenditure in humans.

Size isn't everything, comparatively speaking

Size isn't everything, comparatively speaking

Sex and strain differences in isotope turnover rates and metabolism in house mice (Mus musculus)

The rate of nutrient incorporation into most organisms is an unknown but important factor in temporally variable systems. We investigate within-species variation in tissue turnover and metabolic rate among house mice ( Mus musculus L., 1758). By establishing a predictive relationship between tissue turnover rate and metabolic rate, field-based studies could more easily estimate tissue turnover rates using metabolic rate as a surrogate. Here, a diet change was administered using male and female mice of two strains (BALB/c and CBA/J) to test whether a predictive relationship was detectable within a species. Resting metabolic rate (mean values of 1.50–3.64 mL O2·h–1·g–1) and metabolic tissue turnover m (0.02–0.07), were significantly different between sexes, but not between strains. Females of both strains exhibited a nitrogen turnover rate significantly faster than males. Females had less mass than males, which could account for the differences in tissue replacement rates between sexes. The difference in metabolic rate within a species (between strains) may not be large enough to affect the rate of tissue turnover, suggesting that field researchers may be able to assume similar turnover rates among same-sex individuals of the same species. However, it may be important to account for sexual dimorphism when studying tissue turnover and metabolism.

Acute dietary nitrate supplementation improves dry static apnea performance

Acute dietary nitrate (NO3−) supplementation has been reported to lower resting blood pressure, reduce the oxygen (O2) cost of sub-maximal exercise, and improve exercise tolerance. Given the proposed effects of NO3− on tissue oxygenation and metabolic rate, it is possible that NO3− supplementation might enhance the duration of resting apnea. If so, this might have important applications both in medicine and sport. We investigated the effects of acute NO3− supplementation on pre-apnea blood pressure, apneic duration, and the heart rate (HR) and arterial O2 saturation (SaO2) responses to sub-maximal and maximal apneas in twelve well-trained apnea divers. Subjects were assigned in a randomized, double blind, crossover design to receive 70ml of beetroot juice (BR; containing ∼5.0mmol of nitrate) and placebo juice (PL; ∼0.003mmol of nitrate) treatments. At 2.5h post-ingestion, the subjects completed a series of two 2-min (sub-maximal) static apneas separated by 3min of rest, followed by a maximal effort apnea. Relative to PL, BR reduced resting mean arterial pressure by 2% (PL: 86±7 vs. BR: 84±6mmHg; P=0.04). The mean nadir for SaO2 after the two sub-maximal apneas was 97.2±1.6% in PL and 98.5±0.9% in BR (P=0.03) while the reduction in HR from baseline was not significantly different between PL and BR. Importantly, BR increased maximal apneic duration by 11% (PL: 250±58 vs. BR: 278±64s; P=0.04). In the longer maximal apneas in BR, the magnitude of the reductions in HR and SaO2 were greater than in PL (P≤0.05). The results suggest that acute dietary NO3− supplementation may increase apneic duration by reducing metabolic costs.

Multimodal Monitoring in Subarachnoid Hemorrhage

In severely injured patients, the immediate goal of resuscitation is restoration and maintenance of adequate tissue metabolism by ensuring sufficient delivery of fuel, typically oxygen and glucose, to meet cellular metabolic demands. In neurocritical care, traditional goals of resuscitation—intracranial pressure (ICP), cerebral perfusion pressure (CPP), and the clinical examination—have been extrapolated from those of general critical care. These variables are analogous to central venous pressure, mean arterial pressure, and urine output and are similarly crude. These distant surrogates for cerebral perfusion do not account for dynamic changes in cerebral autoregulation, tissue metabolic rate, cellular fuel use, and microcirculatory dysfunction, all of which impact tissue metabolic health. Although standard, it seems intuitively obvious that a uniform approach of maintaining ICP 60 mm Hg is overly simplistic. This approach does not address either significant baseline differences in patient physiology nor the complex, dynamic, and variable pathophysiological changes that ensue after severe brain injury. A more tailored therapeutic strategy that responds to multiple simultaneously measured and more relevant physiological variables is logically appealing. Until recently, however, the requisite individual patient physiology was inaccessible at the bedside. The emergence of technology that allows for continuous real-time bedside monitoring of cerebral physiology marks a new era in neurocritical care. These monitors facilitate assessment of therapeutic efficacy and may provide more relevant physiological end points for resuscitation. Combining these monitors in a multimodal approach allows for the practice of goal-directed cerebral resuscitation that emphasizes the individual patient's unique neurological and systemic physiology. Aneurysmal subarachnoid hemorrhage (SAH) is an example of a disease in which individualized goal-directed cerebral resuscitation using multimodality neuromonitoring might influence therapy and outcome. After initial patient stabilization and aneurysm exclusion from the circulation, care focuses on prevention of secondary neuronal injury. Of those who survive the initial hemorrhage, …

Distinct hepatic lipid profile of hypertriglyceridemic mice determined by easy ambient sonic-spray ionization mass spectrometry

Easy ambient sonic-spray ionization mass spectrometry (EASI-MS) was used to interrogate the hepatic lipid profiles of hypertriglyceridemic and control normotriglyceridemic mice. The analyses of ex vivo complex lipid mixtures were made directly with EASI-MS without accompanying separation steps. Intense ions for phosphatidylcholines and triacylglycerols were observed in the positive ion mode whereas the spectra in the negative ion mode provided profiles of phosphatidylethanolamines and phosphatidylinositol. EASI-MS was coupled to high-performance thin-layer chromatography for analysis of free fatty acids. Fourier transform-ion cyclotron resonance-mass spectrometry was also employed to confirm the identity of the detected lipids. We demonstrated higher incorporation of oleic acid in phosphatidylcholine and triacylglycerol composition, higher relative abundance of arachidonic acid containing phosphatidylinositol, and overall distinct free fatty acid profile in the livers of genetic hypertriglyceridemic mice. We propose that these alterations in liver lipid composition are related to the higher tissue and body metabolic rates described in these hypertriglyceridemic mice.

Effects of Nonuniform Tissue Properties on Temperature Prediction in Magnetic Nanohyperthermia

In tumor hyperthermia, effectively planning in advance and thus controlling in situ the heating dosage within the target region are rather critical for the success of a therapy. Many studies have simulated the temperature distribution during hyperthermia. However, most of them are based on fixed and known heat source distributions, which are generally very complex to compute. Besides, there is little information concerned the numerical analysis of temperature during magnetic hyperthermia loading with magnetic nanoparticles (MNPs), which has its specific heat source distribution features. Particularly, the parameters for different human tissues varied very much, which will cause a serious impact on the heat source and temperature distribution. This paper is aimed at investigating the effects of nonuniform tissue properties to the temperature prediction in magnetic nanohyperthermia and other possible effect factors including external EM field, MNP properties, tumor size and depth, surface cooling conditions, etc. It was found that the spatial heat source generated in the nonuniform model appears smaller than that in the uniform model. This is mainly resulted from the energy reflection when transmitting from fat to tumor and muscle under the same condition, while the temperature is higher on account of overall contribution of different parameters including tissue thermal conductivity, blood perfusion, density, heat capacity, and metabolic heat production rate, which also affect the temperature distribution apart from the heat source. Controlling the properties of the external EM field, MNPs and cooling water can acquire different temperature distributions. Tumors with different depths and sizes need specific plannings, which require as accurate as possible temperature prediction. The nonuniform model can be further improved to be applied in magnetic nanohyperthermia treatment planning and thus help optimize the surgical procedures.

Resting Energy Expenditure Can Be Assessed by Fat-Free Mass in Female Athletes Regardless of Body Size

Energy requirements can be estimated from resting energy expenditure (REE). However, little is known about factors influencing REE in Japanese female athletes. This study was performed to evaluate the relationship between REE and body composition in Japanese female athletes with a wide range of body sizes. Ninety-three athletes (age 20.3±1.2 y, height 162.8±6.4 cm, body weight (BW) 57.0±9.2 kg, fat-free mass (FFM) 45.4±6.2 kg) were classified into three groups according to BW: small-size (S) (n=34), medium-size (M) (n=34), and large-size (L) (n=25). Systemic and regional body compositions (skeletal muscle (SM), fat mass (FM), bone mass (BM), and residual mass (RM)) were estimated by dual energy X-ray absorptiometry (DXA). Measured resting energy expenditure (REEm) was evaluated by indirect calorimetry. Marked differences were found in REEm (S: 1,111±150, M: 1,242±133, L: 1,478±138 kcal/d), and systemic and regional body compositions among the three groups. REEm was strongly correlated with FFM, and absolute values of RM and SM increased significantly according to body size. There was good agreement between REEm and estimated REE (REEe) from the specific metabolic rates of four major organ tissue level compartments. These data indicate that REE for female athletes can be attributed to changes in organ tissue mass, and not changes in organ tissue metabolic rate. That is, change in REE can be explained mainly by the change in FFM, and REE can be assessed by FFM in female athletes regardless of body size.

Mild Hypothermia as a Cardioprotective Approach for Acute Myocardial Infarction: Laboratory to Clinical Application

In many animal models, mild therapeutic hypothermia is a powerful intervention, reducing myocardial infarct size, reducing the no-reflow phenomenon, and improving healing after infarction. Cooling in these models has been produced by various means including whole-body hypothermia, synchronized hypothermic coronary venous retro-perfusion, heat exchangers, and regional hypothermia targeting the heart alone. However, in humans, the most widely used techniques are surface cooling and cooling by endovascular heat-exchange catheters. The reduction in temperature necessary to produce cardioprotection is mild (32-34°C), appears to have no detrimental effects on left ventricular function or regional myocardial blood flow, and may improve microvascular reflow to previously ischemic heart tissue. It has been shown in experimental and clinical studies that for therapeutic hypothermia to be effective it must be (1) initiated as early as possible after the onset of ischemia and (2) initiated before reperfusion. This may require initiation of hypothermia in the ambulance, well before mechanical reperfusion occurs. The mechanisms of protection produced by hypothermia have yet to be conclusively determined but may include a decrease in tissue metabolic rate, preservation of high energy phosphates, a reduction in tissue apoptosis or induction of heat shock proteins.

Nitrogen and phosphorus allocation in leaves, twigs, and fine roots across 49 temperate, subtropical and tropical tree species: a hierarchical pattern

Summary 1. Hierarchical branching is a fundamental feature of trees. Understanding how tree architecture is linked to tissue nutrient concentrations, metabolic rates, and life cycles is important for predicting ecosystem processes such as respiration, module turnover, and organic matter decomposition. 2. Here, we examined branch order–nutrient relationships in above‐ and belowground tree branching systems by analysing nitrogen (N), phosphorus (P), and N : P ratio in leaves, the first three orders of twigs, and the first five orders of roots in 49 tree species, including 21 temperate angiosperm species, six temperate gymnosperm species, and 22 subtropical‐tropical angiosperm species. 3. Tissue [N] and [P] declined linearly with increasing twig and root orders across all species. The slope of the linear regression between root order and root [N] was the same between temperate and subtropical‐tropical angiosperms, but steeper in angiosperms than gymnosperms. In contrast, root order–[P] relationship differed between biomes but not between phylogenetic groups, probably due to the significantly lower P availability in subtropical‐tropical soils. Additionally, the magnitude of change in tissue [N] and [P] between successive shoot and root branch orders was not constant across branching levels. Among all fine root orders, first order root tips had [N], [P], and N : P ratio most similar to those of leaves. 4. These results demonstrate that there is a general inverse order–nutrient relationship in above‐ and belowground modules, though specific patterns of this relationship differed between N and P, and between species groups. Moreover, among all root orders within the fine root guild, root tips are the best parallels of leaves in nutrient concentrations. The order–nutrient relationships presented here advances our understanding of functional module construction in trees, and provide a basis for modelling tissue chemistry‐regulated processes such as respiration and decomposition in forest ecosystems.

Metabolic depression during aestivation in Cyclorana alboguttata

The green striped burrowing frog, Cyclorana alboguttata, spends, on average, nine to ten months of every year in aestivation. Recently, C. alboguttata has been the focus of much investigation regarding the physiological processes involved in aestivation, yet our understanding of this frog's capacity to metabolically depress remains limited. This study aimed to extend our current knowledge of metabolic depression during aestivation in C. alboguttata. C. alboguttata reduced whole animal metabolism by 82% within 5 weeks of aestivation. The effects of aestivation on mass specific in vitro tissue metabolic rate (VO 2) varied among individual organs, with muscle and liver slices showing significant reductions in metabolism; kidney VO 2 was elevated and there was no change in the VO 2 of small intestine tissue slices. Organ size was also affected by aestivation, with significant reductions in the mass of all tissues, except the gastrocnemius. These reductions in organ size, combined with changes in mass specific VO 2 of tissue slices, resulted in further energy savings to aestivating animals. This study shows that C. alboguttata is capable of selectively down- or up-regulating individual tissues, using both changes in metabolic rate and morphology. This strategy allows maximal energy savings during aestivation without compromising organ functionality and survival at arousal.

Microcirculatory changes and skeletal muscle oxygenation measured at rest by non-infrared spectroscopy in patients with and without diabetes undergoing haemodialysis

IntroductionHaemodialysis has direct and indirect effects on skin and muscle microcirculatory regulation that are severe enough to worsen tolerance to physical exercise and muscle asthenia in patients undergoing dialysis, thus compromising patients' quality of life and increasing the risk of mortality. In diabetes these circumstances are further complicated, leading to an approximately sixfold increase in the incidence of critical limb ischaemia and amputation. Our aim in this study was to investigate in vivo whether haemodialysis induces major changes in skeletal muscle oxygenation and blood flow, microvascular compliance and tissue metabolic rate in patients with and without diabetes.MethodsThe study included 20 consecutive patients with and without diabetes undergoing haemodialysis at Sant Andrea University Hospital, Rome from March to April 2007. Near-infrared spectroscopy (NIRS) quantitative measurements of tissue haemoglobin concentrations in oxygenated [HbO2] and deoxygenated forms [HHb] were obtained in the calf once hourly for 4 hours during dialysis. Consecutive venous occlusions allowed one to obtain muscular blood flow (mBF), microvascular compliance and muscle oxygen consumption (mVO2). The tissue oxygen saturation (StO2) and content (CtO2) as well as the microvascular bed volume were derived from the haemoglobin concentration. Nonparametric tests were used to compare data within each group and among the groups and with a group of 22 matched healthy controls.ResultsThe total haemoglobin concentration and [HHb] increased significantly during dialysis in patients without and with diabetes. Only in patients with diabetes, dialysis involved a [HbO2], CtO2 and increase but left mVO2 unchanged. Multiple regression StO2 analysis disclosed a significant direct correlation of StO2 with HbO2 and an inverse correlation with mVO2. Dialysis increased mBF only in diabetic patients. Microvascular compliance decreased rapidly and significantly during the first hour of dialysis in both groups.ConclusionsOur NIRS findings suggest that haemodialysis in subjects at rest brings about major changes in skeletal muscle oxygenation, blood flow, microvascular compliance and tissue metabolic rate. These changes differ in patients with and without diabetes. In all patients haemodialysis induces changes in tissue haemoglobin concentrations and microvascular compliance, whereas in patients with diabetes it alters tissue blood flow, tissue oxygenation (CtO2, [HbO2]) and the metabolic rate (mVO2). In these patients the mVO2 is correlated to the blood supply. The effects of haemodialysis on cell damage remain to be clarified. The absence of StO2 changes is probably linked to an opposite [HbO2] and mVO2 pattern.

Opioids as triggers for metabolic depression in the frog, Cyclorana alboguttata

Many species of Australian arid zone frogs survive the dry winter months by burrowing underground and entering a state of metabolic depression known as aestivation. While in aestivation these frogs can survive months to years in the absence of food and water, yet the endogenous mechanisms involved in initiation and maintenance of metabolic depression remain poorly understood. The aim of this study was to investigate the potential role of opioids in initiating a metabolic depression in the aestivating frog, Cyclorana alboguttata. To do this we took a two fold approach. First, the presence of opioid receptors was confirmed using PCR and degenerate primers designed from known opioid receptor sequences. Secondly, we used closed box respirometry to measure the direct effects of opioid agonists on tissue metabolic rate. The delta opioid DADLE was found to decrease oxygen consumption of liver and muscle slices by 20% and 25%, respectively, compared to control slices, whereas the kappa opioid Dynorphin A and the mu opioid Morphiceptin had no effect on tissue metabolic rate. This is the first time that opioids have been shown to directly affect metabolic rate in an aestivating species, indicating that endogenous opioids may play an important role in initiating a metabolic depression. Copyright © 2008 Published by Elsevier Inc.

Early brain temperature elevation and anaerobic metabolism in human acute ischaemic stroke

Early after acute ischaemic stroke, elevation of brain temperature might augment tissue metabolic rate and conversion of ischaemic but viable tissue to infarction. This might explain the observed link between pyrexia, severe stroke and poor outcome. We tested this hypothesis by measuring brain temperature and lactate concentration with multi-voxel magnetic resonance spectroscopic imaging across the acute ischaemic stroke lesion and normal brain as determined on diffusion imaging. We compared patterns of lactate concentration (reported in 'institutional units') and temperature elevation in diffusion lesion core, potential penumbra, ipsilateral and contralateral normal brain and with stroke severity. Amongst 40 patients with moderate to severe acute stroke imaged up to 26 h after onset, lactate concentration was highest in the ischaemic lesion core (42 versus 26 units in potential penumbra, P < 0.05), whereas temperature was highest in the potential penumbra (37.7 versus 37.3 degrees C in lesion core, P < 0.05). Neither sub-regional temperature nor lactate concentration correlated with stroke severity. With increasing time after stroke, ipsilateral brain temperature did not change, but contralateral hemisphere temperature was higher in patients scanned at later times; lactate remained elevated in the lesion core, but declined in potential penumbral and ipsilateral normal tissue at later times. We conclude that early brain temperature elevation after stroke is not directly related to lactate concentration, therefore augmented metabolism is unlikely to explain the relationship between early pyrexia, severe stroke and poor outcome. Early brain temperature elevation may result from different mechanisms to those which raise body temperature after stroke. Further studies are required to determine why early brain temperature elevation is highest in potential penumbral tissue.