MRI/MRS of corpus callosum in patients with clinically isolated syndrome suggestive of multiple sclerosis

A trophy of corpus callosum (C C) related to axonal loss has previously been observed in patients at the early stage of clinically definite multiple sclerosis (CDMS). Atrophy increases with the progression of the disease. Nevertheless, no data concerning the onset of atrophy of C C are currently available. The purpose of this study is to determine if damage in callosal tissue was present at the earliest stage of MS, in a subgroup of patients presenting with a clinically isolated syndrome suggestive of MS (C ISSMS), fulfilling the dissemination in space criteria according to McDonald. Magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS) techniques were applied to measure C C volume, magnetization transfer ratio (MTR), mean diffusivity (MD), N-acetyl aspartate/choline-containing compounds (NAA/C ho) ratio, N-acetyl aspartate/total creatine (NA A/C r) ratio and C ho/C r ratio inside the C C of 46 C ISSMS patients and 24 sexand age-matched controls. No atrophy of C C was observed in the C ISSMS group. C C of patients was character ized by decreased MTR and increased MD. No change in the NA A/C r ratio was observed while the NA A/C ho ratio decreased and C ho/C r ratio increased in the splenium and the central anterio r part of C C. These abnormalities were present in patients with, but also without, macroscopic lesions inside the C C. O ur results indicate that diffuse structural and metabolic changes, which may be interpreted as representing predominantly myelin patho logy, occur in the C C at the earliest stage of MS before any atrophy is detected.

Onset and underpinnings of white matter atrophy at the very early stage of multiple sclerosis - a two-year longitudinal MRI/MRSI study of corpus callosum

Backgrounds Atrophy of corpus callosum (CC), a white matter structure linking the two hemispheres, is commonly observed in multiple sclerosis (MS). However, the occurrence and processes leading to this alteration are not yet determined.

Goal and methods To better characterize the onset and progression of CC atrophy from the early stage of MS, we performed a two-year follow-up magnetic resonance imaging/magnetic resonance spectroscopic imaging (MRI/MRSI) exploration of CC in 24 patients with clinically isolated syndrome. These patients were explored using the same protocol at month (M)6, M12 and M24. MRI/MRSI techniques were applied to measure CC volume, and relative concentrations of N-acetylaspartate (NAA), creatine/phosphocreatine (Cr) and choline-containing compounds (Cho). A group of matched controls was also explored.

Results Atrophy of CC, not present at baseline, was observed at M12 and progressed over the second year (M24). At baseline, a decrease in relative NAA level was observed in the anterior and posterior body of CC, with normalization during the follow-up period. In the anterior body, an increase in relative Cho level was observed, with normalization at M6. Normal relative Cr levels were observed at all time points in all sub-regions. The rate of CC atrophy was correlated with the change in the Expanded Disability Status Scale (EDSS) during the follow-up period.

Conclusion These results suggest that CC atrophy appears over a period of one year after the first acute inflammatory episode, and that this atrophy is accompanied, especially in the anterior body of CC, by a normalization of the relative Cho levels, marker of acute inflammation, and NAA levels, marker of neuronal dysfunction and/or loss.

In vivo and in vitro investigations of heterozygous nebulin knock-out mice disclose a mild skeletal muscle phenotype

Nemaline myopathy is the most common congenital skeletal muscle disease, and mutations in the nebulin gene account for 50% of all cases. Recent studies suggest that the disease severity might be related to the nebulin expression levels. Considering that mutations in the nebulin gene are typically recessive, one would expect that a single functional nebulin allele would maintain nebulin protein expression which would result in preserved skeletal muscle function. We investigated skeletal muscle function of heterozygous nebulin knock-out (i.e., nebulin(+/-)) mice using a multidisciplinary approach including protein and gene expression analysis and combined in vivo and in vitro force measurements. Skeletal muscle anatomy and energy metabolism were studied strictly non-invasively using magnetic resonance imaging and 31P-magnetic resonance spectroscopy. Maximal force production was reduced by around 16% in isolated muscle of nebulin(+/-) mice while in vivo force generating capacity was preserved. Muscle weakness was associated with a shift toward a slower proteomic phenotype, but was not related to nebulin protein deficiency or to an impaired energy metabolism. Further studies would be warranted in order to determine the mechanisms leading to a mild skeletal muscle phenotype resulting from the expression of a single nebulin allele.

Multimodal MR imaging (diffusion, perfusion, and spectroscopy): is it possible to distinguish oligodendroglial tumor grade and 1p/19q codeletion in the pretherapeutic diagnosis?

BACKGROUND AND PURPOSE

Pretherapeutic determination of tumor grade and genotype in grade II and III oligodendroglial tumors is clinically important but is still challenging. Tumor grade and 1p/19q status are currently the 2 most important factors in therapeutic decision making for patients with these tumors. Histopathology and cMRI studies are still limited in some cases. In the present study, we were interested in determining whether the combination of PWI, DWI, and MR spectroscopy could help distinguish oligodendroglial tumors according to their histopathologic grade and genotype.

MATERIALS AND METHODS

We retrospectively reviewed 50 adult patients with grade II and III oligodendrogliomas and oligoastrocytomas who had DWI, PWI, and MR spectroscopy at short and long TE data and known 1p/19q status. Univariate analyses and multivariate random forest models were performed to determine which criteria could differentiate between grades and genotypes.

RESULTS

ADC, rCBV, rCBF, and rK2 were significantly different between grade II and III oligodendroglial tumors. DWI, PWI, and MR spectroscopy showed no significant difference between tumors with and without 1p/19q loss. Separation between tumor grades and genotypes with cMRI alone showed 31% and 48% misclassification rates, respectively. Multimodal MR imaging helps to determine tumor grade and 1p/19q genotype more accurately (misclassification rates of 17% and 40%, respectively).

CONCLUSIONS

Although multimodal investigation of oligodendroglial tumors has a lower contribution to 1p/19q genotyping compared with cMRI alone, it greatly improves the accuracy of grading of these neoplasms. Use of multimodal MR imaging could thus provide valuable information that may assist clinicians in patient preoperative management and treatment decision making.

Metabolic profiling in multiple sclerosis and other disorders by quantitative analysis of cerebrospinal fluid using nuclear magnetic resonance spectroscopy

Cerebrospinal fluid (CSF) is being analyzed for the diagnosis of a variety of neurological diseases. Among the methods employed, metabolomics and proteomics are increasingly gaining popularity. At present, sensitivity and, in particular, specificity are limited in CSF metabolomics by nuclear magnetic resonance (NMR) spectroscopy. Nonetheless, progress is being made by studying more and more well-defined and homogeneous patient cohorts. This review starts off with a brief overview of classical CSF analysis in multiple sclerosis (MS), followed by a description of NMR spectroscopy in general metabolic CSF analysis. The subsequent sections focus on metabolomic profiling of CSF by NMR spectroscopy in MS and other neurological disorders. Currently existing results are reviewed and compared, and the potential and limits of this approach are discussed. In addition, several methodological questions are addressed, and the prospects for future developments are briefly outlined.

Is brain maturation comparable in fetuses and premature neonates at term equivalent age?

BACKGROUND AND PURPOSE

Improved knowledge of brain maturation in fetuses and premature neonates is crucial for the early detection of pathologies and would help determine whether MR data from the premature brain might be used to evaluate fetal maturation. Using diffusion-weighted MR imaging and (1)H-MR spectroscopy, we compared cerebral microstructure and metabolism in normal in utero fetuses imaged near term and premature neonates imaged at term equivalent.

MATERIALS AND METHODS

Forty-eight subjects were investigated: 24 in utero fetuses (mean gestational age, 37 ± 1 weeks) and 24 premature neonates (mean postconceptional age, 37 ± 1 weeks). ADC values were measured in cerebellum, pons, white matter, brain stem, basal ganglia, and thalamus. MR spectroscopy was performed in deep white matter.

RESULTS

Mean ADC values from fetuses and premature neonates were comparable except for the pons and the parietal white matter. ADC values were lower in the pons of premature neonates, whereas greater values were found in their parietal white matter compared with fetuses. Proton MR spectroscopy showed higher levels of NAA/H(2)O, Glx/H(2)O, tCr/H(2)O, and mIns/H(2)O in premature neonates compared with fetuses.

CONCLUSIONS

Our study provides evidence of subtle anomalies in the parietal white matter of healthy premature neonates. In addition, the reduced ADC values in the pons together with the increased levels of NAA/H(2)O, tCr/H(2)O, and Glx/H(2)O in the centrum semiovale suggest a more advanced maturation in some white matter regions. Our results indicate that MR data from the premature brain are not appropriate for the assessment of the fetal brain maturation.

Expression of the three nitric oxide synthase isoforms and nitric oxide level in the rat heart during cold storage and blood reperfusion

Maintenance of nitric oxide (NO) homeostasis is an important concept for myocardial protection. Here, we have investigated the NO pathway by analysing total nitrate concentration (NOx) and NO synthase (NOS) isoforms expression as well as the myocardial integrity by lactate dehydrogenase and creatine kinase contents in the rat heart graft arrested by CRMBM solution, submitted to 3 hr cold ischemia in the same solution and 24 hr blood reperfusion following heterotopic abdominal heart transplantation. NOx level was similar to baseline value after ischemia and significantly increased after 24 hr reperfusion. NOS isoforms expression was highly modulated after cold ischemia followed by blood reperfusion. Endothelial NOS expression was decreased after ischemia but restored after 24 hr reperfusion. Neuronal NOS expression was drastically decreased after ischemia and 24 hr reperfusion. Inducible NOS protein was present only after 24 hr reperfusion. Cold ischemia induced a severe loss of creatine kinase without any modification after blood reperfusion. In conclusion, we show here that CRMBM solution did not increase NO production during ischemia but induced an enhanced synthesis of NO during reperfusion which may be related to restoration of endothelial NOS expression and/or induction of inducible NOS expression.

Efficiency of cognitive control recruitment in the very early stage of multiple sclerosis: a one-year fMRI follow-up study

Functional magnetic resonance imaging (FMRI) studies have established that patients with multiple sclerosis show stronger activation in the lateral prefrontal cortices (LPFC) than healthy control subjects during effortful cognitive tasks. The aim of the present study was to assess the impact of these activation changes on cognitive performances. In addition to 19 controls, who were tested at a single time-point to define a standard pattern of fMRI activation during the performance of the Paced Auditory Serial Addition Task (PASAT), 13 patients with clinically isolated syndrome underwent a longitudinal fMRI examination while performing the PASAT at the beginning of the study (M0) and one year later (M12). Relative to the M0 scores, PASAT performances improved in eight patients (group A) and either decreased ( n = 4) or remained unchanged ( n = 1) (group B) in five patients at M12. Random effect analyses (SPM2; Wellcome Institute, London, England) were performed to compare intra-group time-related effects on brain activation (paired t-test between M0 and M12), and inter-group differences were also compared between the two groups of patients (analysis of covariance with PASAT performances as the covariate). Relative to group B, group A showed larger increase in activation between M0 and M12 in the right LPFC. In the whole group of patients, interaction analyses showed that the differences in the PASAT scores between M0 and M12 were correlated with the differences in activation observed in the right LPFC. This longitudinal study shows that in patients with early multiple sclerosis, the increased levels of activation in the right LPFC was associated with improved individual working memory and processing speed performances.

Downregulation of uncoupling protein-3 in vivo is linked to changes in muscle mitochondrial energy metabolism as a result of capsiate administration

Although it has been suggested that the skeletal muscle mitochondrial uncoupling protein-3 (UCP3) is involved in regulating energy expenditure, its role is still poorly understood. In the present study, we aimed at investigating noninvasively, using magnetic resonance techniques, metabolic changes occurring in exercising muscle as a result of capsiate treatment, which has been previously linked to UCP3 upregulation. We showed that capsiate ingestion strongly reduced UCP3 gene expression in rat gastrocnemius muscle. This large underexpression was accompanied by a significant increase in the rate of mitochondrial ATP production and phosphocreatine level both at rest and during muscle stimulation. Similarly, the stimulation-induced ATP fall and ADP accumulation were significantly less after capsiate administration than in untreated rats. The larger oxidative ATP production rate could not be explained by a proportional decrease in the anaerobic component, i.e., glycolysis and phosphocreatine breakdown. In addition, the mechanical performance was not affected by capsiate administration. Finally, the plasma free fatty acid (FFA) level increased in capsiate-treated rats, whereas no significant change was observed after muscle stimulation in the control group. Considering the corresponding enhanced UCP3 mRNA expression occurring in the control group after muscle stimulation, one can suggest that changes in FFA level and UCP3 mRNA expression are not mechanistically correlated. Overall, we have shown that capsiate administration induced a UCP3 downregulation coupled with an increased mitochondrial ATP synthesis, whereas the muscle force-generating capacity was unchanged. This suggests that a decrease in muscle efficiency and/or additional noncontractile ATP-consuming mechanisms result from UCP3 downregulation.

[Indications for cerebral MR proton spectroscopy in 2007]

Magnetic resonance spectroscopy (MRS) is being increasingly performed alongside the more conventional MRI sequences in the exploration of neurological disorders. It is however important to clearly differentiate its clinical applications aiming at improving the differential diagnosis or the prognostic evaluation of the patient, from the research protocols, when MRS can contribute to a better understanding of the pathophysiology of the disease or to the evaluation of new treatments. The most important applications in clinical practice are intracranial space occupying lesions (especially the positive diagnosis of intracranial abscesses and gliomatosis cerebri and the differential diagnosis between edema and tumor infiltration), alcoholic, hepatic, and HIV-related encephalopathies and the exploration of metabolic diseases. Among the research applications, MRS is widely used in multiple sclerosis, ischemia and brain injury, epilepsy and neuro degenerative diseases.

Segmentation of fascias, fat and muscle from magnetic resonance images in humans: the DISPIMAG software

Segmentation of human limb MR images into muscle, fat and fascias remains a cumbersome task. We have developed a new software (DISPIMAG) that allows automatic and highly reproducible segmentation of lower-limb MR images. Based on a pixel intensity analysis, this software does not need any previous mathematical or statistical assumptions. It displays a histogram with two main signals corresponding to fat and muscle, and permits an accurate quantification of their relative spatial distribution. To allow a systematic discrimination between muscle and fat in any subject, fixed boundaries were first determined manually in a group of 24 patients. Secondly, an entirely automatic process using these boundaries was tested by three operators on four patients and compared to the manual approach, showing a high concordance.

Spectroscopie par résonance magnétique des tumeurs cérébrales

MR spectroscopy (MRS) can complement MRI in the evaluation of intracranial tumors. Before treatment, MRS can contribute to the differential diagnosis between tumor and non tumoral lesion (especially intracranial abscesses), to assess the aggressiveness of a glial tumor or to determine its extension to better delineate the surgical removal or the target volume of radiotherapy. During treatment follow-up, MRS helps differentiate recurrent tumor from radionecrosis or physiological post-surgical contrast enhancement. The current studies are trying to determine if the indications of MRS, alone or in association with other MR sequences can further be extended in the study of brain tumors, in particular the follow-up of lesions undergoing chemo or radiotherapy.

[Non-invasive investigation of muscle function using 31P magnetic resonance spectroscopy and 1H MR imaging]

31P MRS and 1H MRI of skeletal muscle have become major new tools allowing a complete non invasive investigation of muscle function both in the clinical setting and in basic research. The comparative analysis of normal and diseased muscle remains a major requirement to further define metabolic events surrounding muscle contraction and the metabolic anomalies underlying pathologies. Also, standardized rest-exercise-recovery protocols for the exploration of muscle metabolism by P-31 MRS in healthy volunteers as well as in patients with intolerance to exercise have been developed. The CRMBM protocol is based on a short-term intense exercise, which is very informative and well accepted by volunteers and patients. Invariant metabolic parameters have been defined to characterize the normal metabolic response to the protocol. Deviations from normality can be directly interpreted in terms of specific pathologies in some favorable cases. This protocol has been applied to more than 4,000 patients and healthy volunteers over a period of 15 years. On the other hand, MRI investigations provide anatomical and functional information from resting and exercising muscle. From a diagnostic point of view, dedicated pulse sequences can be used in order to detect and quantify muscle inflammation, fatty replacement, muscle hyper and hypotrophy. In most cases, MR techniques provide valuable information which has to be processed in conjunction with traditional invasive biochemical, electrophysiological and histoenzymological tests. P-31 MRS has proved particularly useful in the therapeutic follow-up of palliative therapies (coenzyme Q treatment of mitochondriopathies) and in family investigations. It is now an accepted diagnostic tool in the array of tests which are used to characterize muscle disorders in clinical routine. As a research tool, it will keep bringing new information on the physiopathology of muscle diseases in animal models and in humans and should play a role in the metabolic characterization of gene and cell therapy.

Nitric oxide pathway after long-term cold storage and reperfusion in a heterotopic rat heart transplantation model

Recent studies have suggested the involvement of the nitric oxide (NO) pathway in ischemia-reperfusion injury related to cardiac transplantation. Herein, we assessed the NO pathway by quantifying endothelial (e) and inducible (i) nitric oxide synthase (NOS) expression and total NOS activity in a rat heart transplant model during cold ischemia with Celsior cardioplegia and reperfusion. Experiments were performed using a modified Lewis-Lewis heterotopic abdominal heart transplantation with 3 or 6 hours of ischemia with or without 1 hour of blood reperfusion. NOS expression and activity were determined using Western blotting and colorimetric assays, respectively, on freeze-clamped hearts after ischemia without (n = 10) or with reflow (n = 12) compared with basal values. Hearts submitted to 3 hours of ischemia and 1 hour of reperfusion showed a postischemic rate pressure product of 5190 +/- 3047 mm Hg/min (reversible ischemia), but no contractility was observed after 6 hours of ischemia. eNOS protein levels were lower after 3 hours of ischemia compared with the basal value (P = .0005) and were further decreased after 6 hours of ischemia (P < .0001 versus basal value and P = .0018 versus 3 hours of ischemia). Reperfusion did not further decrease eNOS protein levels. iNOS protein was not detected in any condition. NOS activity was increased after 3 hours of ischemia versus basal value (P = .0065) but not after 6 hours of ischemia without any effect of reperfusion. We concluded that eNOS expression was altered during ischemia and the amplitude of the alteration depended on the duration of ischemia. Reversible ischemia was associated with increased NOS activity at the end of ischemia with no variation at reperfusion.

In vivo and in vitro characterization of skeletal muscle metabolism in patients with statin-induced adverse effects

OBJECTIVE

Statins (3-hydroxymethylglutaryl-coenzyme A reductase inhibitor) are widely used to treat hypercholesterolemia. They are generally well tolerated, but myotoxic effects have been reported and the corresponding mechanisms are still a matter of debate. The aim of the present study was to determine whether impairment of calcium homeostasis and/or mitochondrial impairment could account for the adverse effects of statins in skeletal muscle.

METHODS

Eleven patients with increased creatine kinase levels and myalgias after statin treatment were evaluated using in vitro contracture tests (IVCTs), histology, and 31P magnetic resonance spectroscopy (31P-MRS).

RESULTS

IVCT results were abnormal in 7 of the 9 patients, indicating an impaired calcium homeostasis. The 31P-MRS investigation disclosed no anomaly at rest, and the aerobic function assessed during the postexercise recovery period was normal. On the contrary, the pH recovery kinetics was significantly slowed down as indicated by a reduced proton efflux, which could be ultimately linked to a failure of calcium homeostasis. Overall, our observations indicate a normal mitochondrial function and raise the possibility that statins may unmask a latent pathology involving an impairment of calcium homeostasis such as malignant hyperthermia (MH).

CONCLUSION

In case of susceptibility to MH, statins treatment must be administered with caution, and signs of adverse effects should be checked.

1H-MRS imaging in intractable frontal lobe epilepsies characterized by depth electrode recording

Presurgical evaluation of frontal lobe epilepsy (FLE) remains a challenging issue and frequently requires invasive depth electrode recording. In this study, we aimed at evaluating the potential usefulness of a non-invasive technique such as proton magnetic resonance spectroscopic imaging ((1)H-MRSI) in the presurgical evaluation of FLE and at investigating the potential electrophysiological correlates of the metabolic disturbances as defined by (1)H-MRSI. We compared the distribution of (1)H-MRSI abnormalities with the electrophysiological abnormalities defined by stereo-electroencephalography (SEEG) recording in 12 patients presenting with several subtypes of FLE. We also used 12 control subjects in order to obtain normative (1)H-MRSI data. We used a multilevel (1)H-MRSI protocol to better sample the principal regions of the frontal lobe. We also applied a metabolic mapping technique allowing a visual display of metabolic data. A significant decrease of both N-acetyl-aspartate/phosphocreatine-creatine and N-acetyl-aspartate/(choline-compounds + phosphocreatine-creatine) ratios was observed in regions involved in the epileptogenic zone (EZ) and/or the irritative zone (IZ) compared to regions without electrical abnormalities in the same patients (P = 0.044 and P = 0.018, respectively), and also compared to controls (P = 0.004 and P = 0.0001, respectively). No significant differences in metabolic ratios were observed between those regions involved in the EZ and those involved in the IZ only. Our results suggest a link between the relative decrease of N-acetyl-aspartate and the EZ as well as the IZ in FLE. Thus, multilevel (1)H-MRSI protocol may add pertinent information during the non-invasive presurgical evaluation of FLE.

Functional MRI study of PASAT in normal subjects

The paced auditory serial addition test (PASAT) is routinely used to evaluate the cognitive part of the multiple sclerosis functional composite (MSFC) score, the new reference index of patient disability. PASAT is sensitive to subtle cognitive impairment related to MS, although the cognitive components of this test still remain unclear. In order to better characterize brain systems involved during this complex task, functional magnetic resonance imaging (fMRI) experiments were conducted during PASAT in a population of ten normal subjects. The paradigm consisted of a series of 61 single-digit numbers delivered every 3 s. After each number, subjects were asked to overt vocalize the result of the addition of the two last numbers heard. A control task consisting of the repetition of the same series of single-digit numbers was used. Statistical group analysis was performed using the random effect procedure (SPM 99). Cortical activation was observed in the left prefrontal cortex, the supplementary motor area, the lateral premotor cortex, the cingulate gyrus, the left parietal lobe, the left superior temporal gyrus, the left temporal pole, and visual associative areas. fMRI activations underlying PASAT were consistent with an involvement of verbal working memory and the semantic memory retrieval network which could be related to arithmetic fact retrieval. This study on normal subjects could provide a base for the understanding of the potential abnormal cortical activation in MS patients performing this test for a cognitive evaluation.

Modulation of effective connectivity inside the working memory network in patients at the earliest stage of multiple sclerosis

fMRI and structural equation modeling (SEM) were used to study effective connectivity inside the working memory network in patients at the earliest stage of multiple sclerosis (MS), while performing paced auditory serial addition test (PASAT), a sensitive task to reveal subtle cognitive impairments related to working memory and information speed processing. The path model used for SEM included bilateral connections between left and right BA 46, left and right BA 40, left and right anterior cingulate cortex (ACC), left BA 44 and left BA 40, right BA 44 and right BA 40, and unidirectional ipsilateral connections from BA 46 to BA 44, from ACC to BA 46, and from ACC to BA 44. Experimental data from the two groups fit accurately the working memory model, in patients [chi20(2) = 13, P = 0.877] as well as in controls [chi20(2) = 13.54, P = 0.853]. The omnibus test indicated a significant difference of model fits in patients and in controls [chi40(2) = 160.07, P < 0.0001]. Connectivity strengths from right BA 46 to left BA 46, from left ACC to left BA 46 were lower in patients than in controls, and higher from right ACC to right BA 46, from left to right and from right to left ACC (stacked model). Effective connectivity inside the working memory network appears altered in patients at the earliest stage of MS. Modulation of effective connectivity is present in patients inside the executive subsystems of working memory, and could be related to adaptive cognitive control processes that may limit the clinical manifestation of MS.

Cine-MRI assessment of cardiac function in mice anesthetized with ketamine/xylazine and isoflurane

Since small-animal MRI generally requires anesthesia, the effect of the anesthetic regimen on the explored organ(s) has to be taken into account for study interpretation. In this work, we assess the influence of ketamine/xylazine and isoflurane anesthesia on left-ventricular (LV) function in the mouse in vivo by cine-MRI. Three groups of animals were anesthetized with ketamine/xylazine (n = 13) and two different concentrations of isoflurane (1.25%, n = 12 and 2.00%, n = 12) delivered in O2/N2O mix. Long- and short-axis cine-MRI was performed to measure end-diastolic volume, stroke volume, ejection fraction and LV wall thickness. Ketamine/xylazine significantly reduced heart rate, cardiac output and wall thickness, but increased stroke volume and end-diastolic volume compared with both isoflurane groups. No differences across all groups were observed in ejection fraction or systolic wall thickening. Breath rate under isoflurane was significantly lower and concentration dependent, whereas heart function was independent of concentration in all measured parameters. These findings are in agreement with echocardiography and catheterization studies. Isoflurane is advantageous for MR studies because it better maintains cardiac function. Taking into account previously obtained myocardial perfusion measurements, isoflurane concentration should, however, be maintained at the minimum required for a stable sleep even if cardiac function is unaffected by higher isoflurane concentrations.

In vivo MR investigation of skeletal muscle function in small animals

In vivo 31P-MRS investigations have been widely used in small animals to study skeletal muscle function under normal and pathological conditions. Paradoxically in these studies, the benefit provided by 31P-MRS in terms of non-invasiveness is lost because of the utilization of experimental setups that integrate invasive devices for inducing muscle contractions and for measuring mechanical performance. These traditional methodologies, which require surgical preparations, have obvious limitations regarding repeatability in the same animal. The purpose of this review is to highlight the technical aspects of the in vivo MR investigations of skeletal muscle function in small animal models. We will more particularly address the issue related to the invasiveness of different procedures used so far in order to show finally that a further step into non-invasiveness can be achieved, in particular with the support of muscle functional 1H-MRI.

Protective effect of a low K+ cardioplegic solution on myocardial Na,K-ATPase activity

Long duration ischemia in hypothermic conditions followed by reperfusion alters membrane transport function and in particular Na,K-ATPase. We compared the protective effect of two well-described cardioplegic solutions on cardiac Na,K-ATPase activity during reperfusion after hypothermic ischemia. Isolated perfused rat hearts (n = 10) were arrested with CRMBM or UW cardioplegic solutions and submitted to 12 hr of ischemia at 4 degrees C in the same solution followed by 60 min of reperfusion. Functional recovery and Na,K-ATPase activity were measured at the end of reperfusion and compared with control hearts and hearts submitted to severe ischemia (30 min at 37 degrees C) followed by reflow. Na,K-ATPase activity was not altered after 12 hr of ischemia and 1 hr reflow when the CRMBM solution was used for preservation (55 +/- 2 micromolPi/mg prot/hr) compared to control (53 +/- 2 micromol Pi/mg prot/hr) while it was significantly altered with UW solution (44 +/- 2 micromol Pi/mg prot/hr, p < 0.05 vs control and CRMBM). Better preservation of Na,K-ATPase activity with the CRMBM solution was associated with higher functional recovery compared to UW as represented by the recovery of RPP, 52 +/- 12% vs 8 +/- 5%, p < 0.05 and coronary flow (70 +/- 2% vs 50 +/- 8%, p < 0.05). The enhanced protection provided by CRMBM compared to UW may be related to its lower K+ content.

Comparative analysis of in vitro contracture tests with ryanodine and a combination of ryanodine with either halothane or caffeine: a comparative investigation in malignant hyperthermia

BACKGROUND

The diagnosis of susceptibility to malignant hyperthermia (MH) is currently performed on muscle biopsies subjected to halothane-caffeine in vitro contracture tests (IVCTs). There is a consensus on our need to improve the diagnostic potential of IVCTs if we are to maximize the information available for research and diagnosis in MH. This study was designed as a pilot comparative study and we aimed at comparing the ryanodine test and new tests using a combination of ryanodine, halothane and caffeine.

METHODS

One hundred and thirty-two subjects (52 MHS and 80 MHN) were included in this study and new IVCTs were performed in additional muscle biopsy specimens. The contracture time-course was compared considering the onset time of contracture (OT) and the time to reach a 10 mN contracture (10T). Cut-off values were determined using ROC analyses.

RESULTS

For the ryanodine test, sensitivity and specificity calculated for OT were 84.6% and 90.4%, respectively, and were better than those obtained using 10T. Combined tests using either caffeine and ryanodine or halothane and ryanodine did provide higher sensitivities (from 85.3 to 93.9%). A better specificity was only observed for the IVC tests combining halothane (cumulated) and caffeine both with ryanodine (93.9% for both). The largest sensitivity was observed when halothane was used as a bolus and combined with ryanodine. The specificity was always larger with the combined tests as compared to the test using ryanodine alone (from 79.1 to 90.9%). This superiority was confirmed, at least in part, when comparing genetic investigations and the results of new tests in a subgroup of subjects.

CONCLUSIONS

This pilot study showed a clear diagnostic potential for new IVC tests combining halothane, the triggering agent of MH, and ryanodine acting at the calcium release channel, and should be considered as a first step in the investigation of combined tests.

High cerebral scyllo-inositol: a new marker of brain metabolism disturbances induced by chronic alcoholism

Cerebral metabolic changes that concur to motor and/or cognitive disorders in actively drinking alcoholics are not well established. We tested the hypothesis that chronic alcoholics exhibit profound alterations in the cerebral metabolism of scyllo-inositol. Brain metabolism was explored in nine actively drinking and 11 recently detoxified chronic alcoholics by in vivo brain (1)H-MRS and in vitro(1)H-MRS of blood serum and cerebrospinal fluid. The cohort was composed of individuals with acute, subacute or chronic encephalopathy or without any clinical encephalopathy. Chronic alcoholism is associated with a hitherto unrecognized accumulation of brain scyllo-inositol. Our results suggest that scyllo-inositol is produced within the central nervous system and shows a diffuse but heterogenous distribution in brain where it can persist several weeks after detoxification. Its highest levels were observed in subjects with a clinically symptomatic alcohol-related encephalopathy. When detected, brain scyllo-inositol takes part in a metabolic encephalopathy since it is associated with reduced N-acetylaspartate and increased creatine. High levels of cerebral scyllo-inositol are correlated with altered glial and neuronal metabolism. Our findings suggest that the accumulation of scyllo-inositol may precede and take part in the development of symptomatic alcoholic metabolic encephalopathy.

Multimodal magnetic resonance imaging of the central nervous system

The physiological and biochemical properties of the diseased brain that can be explored with magnetic resonance imaging (MRI) are increasing. Progress in MR-based technology affords a large panel of MRI sequences that explore different phenomena and, thus, provide complementary informations. The diagnostic accuracy of MRI is improved by the combination of all MR modalities. However, this abundance of data requires an efficient multiparametric analysis to fully achieve the goal of the multimodal strategy. We will discuss the potential impact of this advanced MRI analysis in the clinical management and the therapeutical strategies of the most common brain pathologies (intracranial tumors, multiple sclerosis, stroke, epilepsy and dementia). This non-invasive approach is of utmost importance since it already improves the diagnosis and the therapeutic choice in the management of several central nervous system diseases.

Modulation of the NO pathway during short or prolonged blood reperfusion following ischaemia in a heterotopic rat heart transplantation model

Ischemia-reperfusion injury plays a major role in graft dysfunction following transplantation. Extensive research has demonstrated that nitric oxide (NO) plays a fundamental role to protect the heart against this injury. Consequently, we quantified NO synthase (NOS) isoform protein levels in a rat heart transplant model during short and prolonged reperfusion following ischemia. Experiments were performed using a modified Lewis to Lewis heterotopic abdominal heart transplantation with a total ischemic time of 3 hours followed by 1 or 24 hours of blood reperfusion (n = 12). Heart function, as represented by the rate pressure product, increased from 7912 +/- 489 to 27067 +/- 9982 mm Hg/min (mean +/- SEM, short vs prolonged reperfusion, P = .0027). NOS isoform protein levels determined using Western blotting of freeze-clamped hearts were compared to baseline values. eNOS protein levels were significantly lower during short reperfusion compared to the basal value (P = .0077) or to prolonged reperfusion (P = .004), returning to the basal value after 24 hours of reflow. iNOS protein was not detected in the basal condition or after 1 hour of reflow, but was present after 24 hours of reflow (P = .0001 vs basal value and 1-hour reflow). nNOS protein was 69% lower after 1 hour of reflow compared with the baseline value (P = .0001), it was not restored after 24 hours of reflow (P = .002). These results suggest involvement of the NO pathway in ischemia-reperfusion injury with distinctive roles of NOS isoforms during short and prolonged reperfusion following ischemia.

Functional investigations of exercising muscle: a noninvasive magnetic resonance spectroscopy-magnetic resonance imaging approach

Muscle fatigue, which is defined as the decline in muscle performance during exercise, may occur at different sites along the pathway from the central nervous system through to the intramuscular contractile machinery. Historically, both impairment of neuromuscular transmission and peripheral alterations within the muscle have been proposed as causative factors of fatigue development. However, according to more recent studies, muscle energetics play a key role in this process. Intramyoplasmic accumulation of inorganic phosphate (P(i)) and limitation in ATP availability have been frequently evoked as the main mechanisms leading to fatigue. Although attractive, these hypotheses have been elaborated on the basis of experimental results obtained in vitro, and their physiological relevance has never been clearly demonstrated in vivo. In that context, noninvasive methods such as 31-phosphorus magnetic resonance spectroscopy and surface electromyography have been employed to understand both metabolic and electrical aspects of muscle fatigue under physiological conditions. Mapping of muscles activated during exercise is another interesting issue which can be addressed using magnetic resonance imaging (MRI). Exercise-induced T2 changes have been used in order to locate activated muscles and also as a quantitative index of exercise intensity. The main results related to both issues, i.e. the metabolic and electrical aspects of fatigue and the MRI functional investigation of exercising muscle, are discussed in the present review.

Preservation of amino acids during long term ischemia and subsequent reflow with supplementation of L-arginine, the nitric oxide precursor, in the rat heart

We investigated whether L-arginine, used in heart preservation to limit endothelial damage, may influence the pool of amino acids during long term ischemia and reflow. Isolated isovolumic rat hearts (n = 23) were submitted to 8 h of hypothermic ischemia after cardioplegic arrest with the Centre de Résonance Magnétique Biologique et Médicale (CRMBM) solution with or without L-arginine (Arg and No Arg groups respectively). Hearts were freeze-clamped after ischemia (n = 11) or submitted to 60 min of reflow (n = 12) and freeze-clamped. Eight hearts were perfused aerobically for 20 min and freeze-clamped (No ischemia group). Addition of L-arginine to the CRMBM solution limited aspartate depletion and decreased lysine level at the end of ischemia. After reflow, L-arginine supplementation increased the pool of glutamate and arginine and limited the depletion of serine, asparagine, glycine and taurine. We conclude that adding L-arginine to the CRMBM cardioplegic solution during long term ischemia preserved the amino acids pool.

Combined in situ analysis of metabolic and myoelectrical changes associated with electrically induced fatigue

Electrical muscle stimulation (Mstim) at a low or high frequency is associated with failure of force production, but the exact mechanisms leading to fatigue in this model are still poorly understood. Using 31P magnetic resonance spectroscopy (31PMRS), we investigated the metabolic changes in rabbit tibialis anterior muscle associated with the force decline during Mstim at low (10 Hz) and high (100 Hz) frequency. We also simultaneously recorded the compound muscle mass action potential (M-wave) evoked by direct muscle stimulation, and we analyzed its post-Mstim variations. The 100-Hz Mstim elicited marked M-wave alterations and induced mild metabolic changes at the onset of stimulation followed by a paradoxical recovery of phosphocreatine (PCr) and pH during the stimulation period. On the contrary, the 10-Hz Mstim produced significant PCr consumption and intracellular acidosis with no paradoxical recovery phenomenon and no significant changes in M-wave characteristics. In addition, the force depression was linearly linked to the stimulation-induced acidosis and PCr breakdown. These results led us to conclude that force failure during 100-Hz Mstim only results from an impaired propagation of muscle action potentials with no metabolic involvement. On the contrary, fatigue induced by 10-Hz Mstim is closely associated with metabolic changes with no alteration of the membrane excitability, thereby underlining the central role of muscle energetics in force depression when muscle is stimulated at low frequency. Finally, our results further indicate a reduction of energy cost of contraction when stimulation frequency is increased from 10 to 100 Hz.

Metabolic counterpart of decreased apparent diffusion coefficient during hyperacute ischemic stroke: a brain proton magnetic resonance spectroscopic imaging study

BACKGROUND AND PURPOSE

Recent studies have shown that the brain ischemic area defined by the map of decreased apparent diffusion coefficient (ADC) obtained by diffusion-weighted imaging (DWI) during the first hours of ischemic stroke includes a significant part of ischemic penumbra. We hypothesize that the misjudgment of the final infarct size by ADC mapping may be related to a restricted ability of DWI to capture variations in the intensity of cellular suffering. In an attempt to characterize metabolically the hypoperfused brain parenchyma, we studied the relationship between ADC values and brain metabolic parameters measured by proton MR spectroscopic imaging (SI).

METHODS

Six patients with hyperacute ischemic stroke were explored within the first 7 hours after onset with the use of a MR protocol including T2*-weighted MRI, DWI, SI, perfusion-weighted imaging, and MR angiography.

RESULTS

This study demonstrates, for the first time, a wide gradient of ischemia-related metabolic anomalies within the abnormal area delineated by DWI during hyperacute ischemic stroke. In the narrow range of decreased mean ADC values (0.60 to 0.40 x 10(-9) m2 x s(-1)), a 33% decrease in mean ADC is associated with a 122% increase in lactate/N-acetyl aspartate ratio. Mean ADC values never fall below 0.40 x 10(-9) m2 x s(-1) within the severely affected ischemic tissue, while SI still detects a large metabolic heterogeneity inside areas showing similar decreased mean ADC values close to this threshold.

CONCLUSIONS

Our results indicate that the region of very low mean ADC values observed during hyperacute ischemic stroke contains areas of various tissue damage intensity characterized by SI in relation to different stages of cellular metabolic injury. This observation may explain why ADC mapping does not reliably predict final infarct size.

Metabolic determinants of the onset of acidosis in exercising human muscle: a 31P-MRS study

Onset of intracellular acidosis during muscular exercise has been generally attributed to activation or hyperactivation of nonoxidative ATP production but has not been analyzed quantitatively in terms of H(+) balance, i.e., production and removal mechanisms. To address this issue, we have analyzed the relation of intracellular acidosis to H(+) balance during exercise bouts in seven healthy subjects. Each subject performed a 6-min ramp rhythmic exercise (finger flexions) at low frequency (LF, 0.47 Hz), leading to slight acidosis, and at high frequency (HF, 0.85 Hz), inducing a larger acidosis. Metabolic changes were recorded using (31)P-magnetic resonance spectroscopy. Onset of intracellular acidosis was statistically identified after 3 and 4 min of exercise for HF and LF protocols, respectively. A detailed investigation of H(+) balance indicated that, for both protocols, nonoxidative ATP production preceded a change in pH. For HF and LF protocols, H(+) consumption through the creatine kinase equilibrium was constant in the face of increasing H(+) generation and efflux. For both protocols, changes in pH were not recorded as long as sources and sinks for H(+) approximately balanced. In contrast, a significant acidosis occurred after 4 min of LF exercise and 3 min of HF exercise, whereas the rise in H(+) generation exceeded the rise in H(+) efflux at a nearly constant H(+) uptake associated with phosphocreatine breakdown. We have clearly demonstrated that intracellular acidosis in exercising muscle does not occur exclusively as a result of nonoxidative ATP production but, rather, reflects changes in overall H(+) balance.

MR spectroscopic pulvinar sign in a case of variant Creutzfeldt-Jakob disease

We report MR spectroscopic findings in a patient hospitalized with biopsy-proven variant Creutzfeldt-Jakob (vCJD) disease. N-acetyl aspartate was markedly decreased in the postero-medial part of the thalami (pulvinar) but was not diminished in the parieto-occipital white matter and cortical grey matter. These observations, which are in accordance with the pathological findings in this disease, suggest that MR spectroscopy, a highly sensitive method for the detection of subtle brain metabolic dysfunction, could be of interest for the diagnosis, prognosis and therapeutic follow-up of vCJD.

Citrulline/malate promotes aerobic energy production in human exercising muscle

BACKGROUND

Previous studies have shown an antiasthenic effect of citrulline/malate (CM) but the mechanism of action at the muscular level remains unknown.

OBJECTIVE

To investigate the effects of CM supplementation on muscle energetics.

METHODS

Eighteen men complaining of fatigue but with no documented disease were included in the study. A rest-exercise (finger flexions)-recovery protocol was performed twice before (D-7 and D0), three times during (D3, D8, D15), and once after (D22) 15 days of oral supplementation with 6 g/day CM. Metabolism of the flexor digitorum superficialis was analysed by (31)P magnetic resonance spectroscopy at 4.7 T.

RESULTS

Metabolic variables measured twice before CM ingestion showed no differences, indicating good reproducibility of measurements and no learning effect from repeating the exercise protocol. CM ingestion resulted in a significant reduction in the sensation of fatigue, a 34% increase in the rate of oxidative ATP production during exercise, and a 20% increase in the rate of phosphocreatine recovery after exercise, indicating a larger contribution of oxidative ATP synthesis to energy production. Considering subjects individually and variables characterising aerobic function, extrema were measured after either eight or 15 days of treatment, indicating chronological heterogeneity of treatment induced changes. One way analysis of variance confirmed improved aerobic function, which may be the result of an enhanced malate supply activating ATP production from the tricarboxylic acid cycle through anaplerotic reactions.

CONCLUSION

The changes in muscle metabolism produced by CM treatment indicate that CM may promote aerobic energy production.

[Non invasive investigation of muscle diseases using 31P magnetic resonance spectroscopy: potential in clinical applications]

P-31 MRS has become in a very short time, a major new tool to explore muscle metabolism for clinical diagnostic purposes, while offering a unique non-invasive way to conduct advanced basic research in muscle physiopathology. The comparative analysis of normal and diseased muscle remains a major requirement to further define metabolic events surrounding muscle contraction and the metabolic anomalies underlying pathologies. Also, standardized rest-exercise-recovery protocols for exploration of muscle metabolism by P-31 MRS in healthy volunteers as well as in patients with intolerance to exercise need to be developed. Our protocol is based on a short term intense exercise which is very informative and well accepted by volunteers and patients. Invariant metabolic parameters have been defined to characterize the normal metabolic response to the protocol. Deviations from normality can be directly interpreted in terms of specific pathologies in some favorable cases. In most cases, P-31 MRS provides valuable information which has to be processed in conjunction with traditional invasive biochemical, electrophysiological and histoenzymological tests. For malignant and exercise hyperthermias, P-31 MRS constitutes a diagnostic tool with 100p.cent sensitivity, as compared to contracture tests on muscle biopsies. P-31 MRS has proved particularly useful in the therapeutic follow-up of palliative therapies (coenzyme Q treatment of mitochondriopathies) and in family investigations. It is now an accepted diagnostic tool in the array of tests which are used to characterize muscle disorders in clinical routine. As a research tool, it will keep bringing new information on the physiopathology of muscle diseases in animal models and in humans and should play a role in the metabolic characterization of gene therapy.

Investigation of fluoroquinolone-induced myalgia using (31)P magnetic resonance spectroscopy and in vitro contracture tests

OBJECTIVE

To investigate muscle function in patients with severe myalgia resulting from fluoroquinolone (FQ) treatment. We used histology, in vitro contracture tests (IVCTs), and (31)P magnetic resonance spectroscopy ((31)P MRS) to explore muscle contraction and metabolism.

METHODS

We studied 3 patients with myalgia, hyperalgia tendinopathy, and arthralgia following FQ treatment and 3 normal subjects after taking FQs. Results were compared with those of a control group of 9 subjects free of any muscle disease and not taking FQs. Muscle biopsies were performed on the left biceps, and IVCTs were performed in accordance with the protocol recommended by the European Malignant Hyperthermia Group. (31)P MR spectra of forearm flexor muscles were recorded at 4.7T throughout a rest-exercise-recovery protocol.

RESULTS

(31)P MRS showed a significant reduction of pH changes measured at the end of exercise and a faster rate of proton efflux measured during recovery in all patients. IVCTs diagnosed 1 patient as being susceptible to malignant hyperthermia. No specific histologic anomalies were observed in muscle biopsy samples, which showed normal mitochondria.

CONCLUSION

The adverse effects recorded in the 3 patients are related to a preexisting muscular anomaly revealed by FQ treatment.

[Applications of magnetic resonance spectrometry (MRS) in the study of metabolic disturbances affecting the brain in alcoholism]

The purpose of this article is to provide an overview of the current applications of magnetic resonance spectroscopy (MRS) to the investigation of cerebral metabolism in alcoholic patients. The specific metabolic changes associated with the intoxication process (tolerance, dependance), abstinence and alcohol-related diseases (alcoholic encephalopathy, cirrhosis, Gayet-Wernicke's encephalopathy, Marchiafava-Bignami syndrome) are described.

In vivo reduction in ATP cost of contraction is not related to fatigue level in stimulated rat gastrocnemius muscle

1. We tested whether the reduction in ATP cost of contraction during in vivo stimulation of rat gastrocnemius muscle was related to fatigue level. 2. Muscles (n = 44) were electrically stimulated to perform 6 min repeated isometric contractions at different frequencies; one non-fatiguing protocol (stimulation at 0.8 Hz) and five fatiguing protocols (2, 3.2, 4, 5.2 and 7.6 Hz) were used. Anaerobic and oxidative ATP turnover rates were measured non-invasively using (31)P-magnetic resonance spectroscopy. 3. At the onset of the stimulation period, no signs of fatigue were measured in the six protocols and ATP cost of contraction did not differ significantly (P = 0.45) among protocols (mean value of 1.76 +/- 0.11 mM (N s)(-1)). 4. For the six protocols, ATP cost of contraction was significantly reduced (P < 0.05) at the end of the stimulation period when compared with the initial value. This reduction did not differ significantly (P = 0.61) among the five fatiguing protocols (averaging 35 +/- 3 % of initial value), whereas isometric force decreased significantly as stimulation frequency increased. No significant correlation (P = 0.87, r(2) = 0.01) was observed between isometric force and ATP cost of contraction at the end of the stimulation period. In addition, this reduction was significantly lower (P < 0.05) for the non-fatiguing protocol (67 +/- 9 % of initial value) when compared with the fatiguing protocols. 5. These results demonstrate that (i) the reduction in ATP cost of contraction during in vivo stimulation of rat gastrocnemius muscle is not related to the fatigue level; (ii) surprisingly, this reduction was significantly larger during the fatiguing protocols compared with the non-fatiguing protocol.

Time-dependent and indirect effect of inorganic phosphate on force production in rat gastrocnemius exercising muscle determined by 31P-MRS

The relationship of inorganic phosphate (P(i)) and its diprotonated form (H(2)PO(4)(-)) to isometric force (F) was analyzed non-invasively using 31P-magnetic resonance spectroscopy. Rat gastrocnemius muscles were electrically stimulated at six different frequencies in order to produce different levels of fatigue. A curvilinear relationship was demonstrated between force production and [P(i)] and [H(2)PO(4)(-)] accumulation. [P(i)] and [H(2)PO(4)(-)] were correlated with F at the end of the stimulation period but not when F was maximal at the early stage of the stimulation period. Interestingly, the respective [P(i)] and [H(2)PO(4)(-)] did not differ significantly between these two stages demonstrating that [P(i)] and [H(2)PO(4)(-)] cannot be considered as direct effectors of fatigue. This time-dependent and indirect effect of [P(i)] and [H(2)PO(4)(-)] on force production might be mediated by calcium ions.

Regional metabolite levels of the normal posterior fossa studied by proton chemical shift imaging

MR spectroscopy of the posterior fossa is pitted with numerous technical difficulties. It is, however, of great clinical interest in the study of the degenerative diseases and tumors of this area. We have developed a method to perform 2D CSI of this area, by using a sagittal slice and a careful positioning of outer volume saturation. We performed this acquisition in 30 healthy volunteers to determine the normal metabolic ratios in five voxels of this area (mesencephalon, pons, medulla oblongata, vermis, cerebellar white matter). The main technical difficulty was magnetic field inhomogeneity in the lower brainstem generated by dental alloys. However, 88% of the voxels were of sufficient quality to be analyzed. The statistically significant regional variations were a higher NAA/Cr ratio in the pons than in the medulla oblongata, higher Cho/Cr in the pons than in the mesencephalon and higher Cho/Cr in the cerebellar white matter than in the vermis. We conclude that 2D CSI of the brainstem, although technically delicate can be performed in most patients.

Interrelations of ATP synthesis and proton handling in ischaemically exercising human forearm muscle studied by 31P magnetic resonance spectroscopy

1. In ischaemic exercise ATP is supplied only by glycogenolysis and net splitting of phosphocreatine (PCr). Furthermore, 'proton balance' involves only glycolytic lactate/H+ generation and net H+ 'consumption' by PCr splitting. This work examines the interplay between these, metabolic regulation and the creatine kinase equilibrium. 2. Nine male subjects (age 25-45 years) performed finger flexion (7 % maximal voluntary contraction at 0.67 Hz) under cuff ischaemia. 31P magnetic resonance spectra were acquired from finger flexor muscle in a 4.7 T magnet using a 5 cm surface coil. 3. Initial PCr depletion rate estimates total ATP turnover rate; glycolytic ATP synthesis was obtained from this and changes in [PCr], and then used to obtain flux through 'distal' glycolysis (phosphofructokinase and beyond) to lactate; 'proximal' flux (through phosphorylase) was obtained from this and changes in [phosphomonoester]. Total H+ load (lactate load less H+ consumption) was used to estimate cytosolic buffer capacity (beta). 4. Glycolytic ATP synthesis increased from near zero while PCr splitting declined. Net H+ load was approximately linear with pH, suggesting beta = 20 mmol x l(-1) (pH unit)(-1) at rest, increasing as pH falls. 5. Relationships between glycolytic rate and changes in [PCr] (i.e. the time-integrated mismatch between ATP use and production), and thus also [P(i)] (substrate for phosphorylase), suggest that increase in glycolysis is due partly to 'open-loop' Ca2+-dependent conversion of phosphorylase b to a, and partly to the 'closed loop' increase in P(i) consequent on net PCr splitting. 6. The 'settings' of these mechanisms have a strong influence on changes in pH and metabolite concentrations.

A noninvasive investigation of muscle energetics supports similarities between exertional heat stroke and malignant hyperthermia

Exertional heat stroke (EHS) is usually triggered by strenuous exercise performed under hot and humid environmental conditions. Although the pathogenesis of an EHS episode differs from that of a clinical malignant hyperthermia (MH) crisis, both conditions share some similarities in symptoms, such as the abnormal increase in core temperature. By use of (31)P magnetic resonance spectroscopy, we analyzed the muscle energetics of 26 post-EHS subjects for whom in vitro halothane/caffeine contracture tests were abnormal and investigated possible similarities with subjects susceptible to MH. An early decrease of pH was noted during the first minute of exercise in EHS subjects as compared with controls. EHS subjects were divided into two subgroups according to the diagnostic score previously developed for MH subjects. The 19 subjects (73%) with a score higher than 2 displayed significantly larger caffeine-induced and earlier ryanodine-induced contractures on muscle biopsies as compared with the rest of the group (7 subjects). The results demonstrate that muscle energetics are abnormal in subjects who have experienced EHS and suggest a possible link between MH and EH, although all EHS cannot be considered as MH.

Malignant hyperthermia susceptibility revealed by myalgia and rhabdomyolysis during fluoroquinolone treatment

Fluoroquinolones cause myalgia, but this complication is not clearly documented. We describe a patient who developed myalgia and rhabdomyolysis during fluoroquinolone treatment. The patient was a 33-year-old man treated with norfloxacin for common cystitis. He complained of general muscular fatigue, tendon disorders, and articular pain during treatment. When the antimicrobial agent was stopped, symptoms decreased, with persistence of slight myalgia for 10 days. Rhabdomyolysis was detected. Six months later, investigation by 31P magnetic resonance spectroscopy revealed an oxidative disorder and an abnormal abundance of phosphomonoesters. In vitro contracture tests led to a diagnosis of malignant hyperthermia susceptibility. Our case shows that for any subject presenting myalgia with rhabdomyolysis triggered by fluoroquinolone treatment, the presence of a latent myopathy should be investigated.