Muscle energy metabolism in McArdle's syndrome by in vivo phosphorus magnetic resonance spectroscopy

Five patients with McArdle's syndrome were examined by phosphorus magnetic resonance spectroscopy (31P-NMR). Adenosine triphosphate (ATP) levels at rest were reduced by 22%, but did not fall further during exercise or contracture. The slope of work rate versus inorganic phosphate/phosphocreatine (Pi/PCr) was 42 +/- 8 joules/min/Pi/PCr in three patients without muscle wasting, compared with 13 and 16 in patients with atrophy (normal, 30 to 50 joules/min/Pi/PCr). Recovery from exercise showed similar rates in patients (postischemic exercise 1.03 +/- 0.17, post-aerobic 1.63 +/- 0.17 PCr/Pi units per minute) and controls (1.0 +/- 0.2 and 1.8 +/- 0.2, respectively) independent of intracellular pH. Infusion of glucose improved exercise kinetics by 163 to 190%, but an oral load of protein had no effect. We conclude that (1) muscle mitochondria operate normally in vivo in this glycogenolytic disorder, suggesting a sufficient alternate fuel supply. (2) Blood-borne glucose may serve as one alternate fuel for the "second wind" phenomenon. (3) ATP control mechanisms are altered only at rest. (4) Recovery from exercise is relatively pH-independent.     

Detection of muscle injury in humans with 31-P magnetic resonance spectroscopy

Strenuous exercise can result in muscle injury that may persist for 2 weeks. Our purpose was to determine if muscle injury can be detected with 31-P magnetic resonance spectroscopy. Normal subjects performed repeated lengthening contractions with either arms or legs designed to result in mild muscle injury. One hour after the arm exercise, there was a significant increase in the inorganic phosphate to phosphocreatine ratio (Pi/PCr), with the maximum increase in Pi/PCr occurring 1 day postexercise (0.12 +/- 0.01 to 0.21 +/- 0.05). Pi/PCr remained elevated for 3-10 days. Similar results were seen following the leg exercise protocol. ATP/(Pi + PCr) decreased in all the arm exercised subjects. Exercise protocols that did not contain lengthening contractions did not result in changes of Pi/PCr or ATP/(Pi + PCr). Patients with various neuromuscular diseases with evidence of muscle damage (elevated CK, muscle soreness, and histopathological findings) also showed increased Pi/PCr at rest. We conclude that elevated Pi/PCr at rest can reflect nonspecific muscle damage in normal and diseased subjects.     

Fuel utilization in subjects with carnitine palmitoyltransferase 2 gene mutations

Patients with the myopathic form of carnitine palmitoyltransferase II (CPT II) deficiency typically experience muscle pain, cramps, and myoglobinuria during prolonged exercise. It has been suggested that carriers of CPT2 gene mutations also may have milder clinical symptoms, but fatty acid oxidation (FAO) has never been investigated in vivo in this group. We studied fuel utilization by indirect calorimetry and stable isotope methodology in four patients with CPT II deficiency, three subjects who carried one CPT2 gene mutation, and five healthy control subjects. Cycle exercise at a constant workload of 50% of maximal oxygen uptake capacity was used to facilitate FAO. We found that in vivo oxidation of long-chain fatty acids was normal at rest but severely impaired during prolonged, low-intensity exercise in patients with CPT II deficiency, and that two of the single CPT2 gene mutation carriers, who displayed symptoms of CPT II deficiency, had an FAO comparable with the patients. These results indicate that residual CPT II activity is sufficient to maintain long-chain FAO at rest in CPT II deficiency but not to increase FAO during exercise. The findings also suggest that single CPT2 gene mutations may exert a dominant-negative effect on the tetrameric CPT II protein.     

ATP, phosphocreatine and lactate in exercising muscle in mitochondrial disease and McArdle's disease

We studied exercise-induced changes in the adenosine triphosphate (ATP), phosphocreatine (PCr), and lactate levels in the skeletal muscle of mitochondrial patients and patients with McArdle's disease. Needle muscle biopsy specimens for biochemical measurement were obtained before and immediately after maximal short-term bicycle exercise test from 12 patients suffering from autosomal dominant and recessive forms of progressive external ophthalmoplegia and multiple deletions of mitochondrial DNA (adPEO, arPEO, respectively), five patients with mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS) 3243 A-->G point mutation, and four patients with McArdle's disease. Muscle ATP and PCr levels at rest or after exercise did not differ significantly from those of the controls in any patient group. In patients with mitochondrial disease, muscle lactate tended to be lower at rest and increase more during exercise than in controls, the most remarkable rise being measured in patients with adPEO with generalized muscle symptoms and in patients with MELAS point mutation. In McArdle patients, the muscle lactate level decreased during exercise. No correlation was found between the muscle ATP and PCr levels and the respiratory chain enzyme activity.     

Partial block of glycolysis in late-onset phosphofructokinase deficiency myopathy

A late-onset, myopathic variant of phosphofructokinase (PFK) deficiency has been previously described in two patients of Ashkenazic descent. We report here on a non-Ashkenazic woman with the onset, at the age of 48 years, of a progressive limb girdle myopathy that was not preceded by a history of exercise intolerance. Muscle biopsy findings at the age of 58 years showed deposition of amylopectin-like material in muscle fibers and the absence of histochemical PFK activity. Enzymatic PFK activity in vitro was only 4% of normal. Since the forearm ischemic exercise test induced a sub-normal production of serum lactate, the patient underwent phosphorus magnetic resonance spectroscopy (³¹P-MRS), a non-invasive method that allows in vivo assessment of the functional status of the glycolytic pathway and mitochondrial oxidative metabolism by measuring the high-energy phosphates and cytosolic pH. In vivo, ³¹P-MRS disclosed a residual glycolytic flux and a normal rate of ATP production both at rest and during exercise. These results suggest that, in some patients, muscle PFK deficiency may be partial in vivo, and more severe in vitro, possibly due to protein or mRNA instability rather than absence. The presence of these findings in a patient with the late-onset myopathic form is compatible with a distinct pathogenetic mechanism, relying on progressive polysaccharide accumulation, rather than on acute energetic shortage in muscle fibers. Received: 4 May 1995 / Revised, accepted: 28 September 1995     

Skeletal muscle mitochondrial dysfunction in alternating hemiplegia of childhood

Alternating hemiplegia of childhood is an uncommon disease characterized by repeated, transient attacks of hemiplegia. Its pathophysiology is uncertain, but attention recently has focused on possible mitochondrial abnormalities. Using ³¹P magnetic resonance spectroscopy, we studied gastrocnemius muscle in 5 patients with alternating hemiplegia, aged 8 to 30 (mean, 18) years, at rest and during incremental aerobic exercise and recovery. There were no significant differences in resting muscle between patients and a control group aged 7 to 42 (mean, 19) years. Exercise performance was grossly impaired in the patients, the mean duration being 30% of normal. The total change in pH during exercise was somewhat less than in control subjects, while the changes in phosphocreatine concentration and intracellular ADP were similar. Thus the average overall rate of fall of phosphocreatine concentration during exercise was three-fold greater than in control subjects. However, the initial rate of ATP turNovemberer at the start of exercise (a measure of muscle mass and efficiency) was not abnormal. During recovery, both the initial rate of phosphocreatine resynthesis and the calculated mitochondrial capacity were reduced by about 35%. This mitochondrial defect probably explains most of the abnormalities seen during exercise.     

Metabolism of rat skeletal muscle after spinal cord transection

We investigated the energy metabolism of the gastrocnemius muscle of the rat after spinal cord transection, using in vivo (31)P magnetic resonance spectroscopy (MRS). Spectra were obtained at rest and during exercise and recovery before, and at different time-points after, spinal cord transection. At rest, the adenosine triphosphate (ATP) level was not altered and the intracellular pH became permanently more alkaline. In electrically stimulated muscle, cord transection caused a greater phosphocreatine depletion than in control animals, and the maximum rate of oxidative ATP synthesis was significantly diminished; at days 30 and 60 after transection, an intracellular acidification was observed at the end of exercise. These effects indicate that, as in humans, spinal cord transection in rats leads to a decrease in mitochondrial oxidative metabolism and probably to an increase in anaerobic metabolism. This experimental model may prove useful for evaluating various approaches to improve muscle function in paraplegia.     

The adaptive response of skeletal muscle to increased use

Skeletal muscle undergoes profound changes in morphological, physiological, and biochemical character when subjected to prolonged periods of increased use. Although increased use may be brought about in a variety of ways, the results show consistent features. In particular, endurance exercise and chronic stimulation differ only in degree: the properties which change in response to exercise are also those which change at an early stage of stimulation; the properties which are resistant to change under exercise conditions change only after prolonged stimulation. There is therefore a hierarchy of stability in the properties of skeletal muscle which is revealed in its response to changing functional demands. The adaptive potential of muscle provedes a logical framework for understanding neural influences on the emergence of fiber types during muscle development. It is also relevant to the study of pathological conditions which may involve a sustained departure from normal postural and locomotor patterns of activity.     

Muscle carnitine deficiency associated with myalgia and rhabdomyolysis following exercise

A case of 16-year-old female with myalgia and myoglobinuria following prolonged exercise was reported. Neurological examination revealed mild weakness of proximal muscle in the lower extremities. Serum CK, LDH, myoglobin were significantly increased during the attacks. On biopsy, the muscle fibers contained myriad lipid-filled vacuoles, in predominantly type 1 fibers. Electron microscope examinations revealed numerous lipid droplets adjacent to mitochondria and glycogen particles. Carnitine level in the patient's muscle was markedly reduced (under 5% of control), but the serum carnitine concentration was normal. The muscle carnitine palmityl transferase level was not depressed. A forearm ischemic test resulted in normal lactate production. On exercise tolerance test by a bicycle ergometer, mild exercise (15-30 watts for 15 minutes) induced myalgia and marked elevation in serum CK, lactate and pyruvate, while severe exercise showed no increase in serum CK level. The findings suggest that the energy production system in the skeletal muscle was impaired. However, the enzyme activities of NADH oxidation in mitochondria and the anaerobic glycolysis pathway were within normal limits. During fasting (36 hours), there was a normal production of ketone bodies, suggesting that hepatic metabolism of lipids was normal. She showed good response to L-carnitine therapy.     

Canine X-linked muscular dystrophy studied with in vivo phosphorus magnetic resonance spectroscopy.

Duchenne muscular dystrophy (DMD) is an X-linked disease characterized by progressive muscle weakness and degeneration. Dystrophin is the product of the missing gene in this disorder. However, the cause of the dystrophic process is not understood. Transient muscle injury is normally seen after muscle exercise, and may be a necessary process in muscle growth and preservation. We, therefore, chose to evaluate the role of exercise in Duchenne dystrophy by studying the canine X-linked animal model (CXMD). These dogs also lack dystrophin and have clinical signs similar to humans. Exercise was initiated by electrical stimulation, and muscle metabolism was monitored with phosphorus magnetic resonance spectroscopy (P-MRS). Dogs with CXMD had abnormal muscle pathology and markedly elevated serum CK. The inorganic phosphate (Pi) to phosphocreatine (PCr) ratio was increased in CXMD dogs at rest compared with normal dogs (Pi/(Pi + PCr) = 0.166 +/- 0.054 for CXMD and 0.073 +/- 0.017 for normals, mean +/- SE). No changes in resting ATP, pH, phosphomonoesters (PME), and phosphodiesters (PDE) were seen. The mean Pi/(Pi + PCr) and pH values during stimulation were normal in the CXMD dogs. Two to three days after electrical stimulation, resting Pi/(Pi + PCr) ratios were significantly increased in the CXMD dogs (0.127 +/- 0.029 compared with 0.172 +/- 0.054, mean +/- SD). Normal dogs showed no increase in Pi/(Pi + PCr) following stimulation. There was a 50-fold greater increase in serum CK in CXMD compared with normal dogs following exercise. These results indicate greater muscle injury in CXMD muscle, and suggest that in the absence of dystrophin, exercise-induced muscle injury may play a role in the dystrophic process.     

A 31P-NMR study of muscle exercise metabolism in mdx mice: evidence for abnormal pH regulation.

We have studied exercise metabolism in vivo in the mdx mouse model of Duchenne muscular dystrophy with 31P-nuclear magnetic resonance spectroscopy. Intracellular pH, ratios of phosphocreatine (PCr) to ATP and PCr to inorganic phosphate (P(i)) expressed as PCr/ATP and PCr/(PCr+P(i)) as well as tension generated at the Achilles tendon were measured during sciatic nerve stimulation. Tension was similar between the mdx and control strain C57Bl/10ScSn at 10 Hz stimulation but slightly higher than the control at 100 Hz. The PCr/ATP and PCr/(PCr+P(i)) ratios were significantly reduced in mdx vs. control muscle during exercise. Although resting muscle pH in mdx mice is more alkaline than normal muscle, the pH of mdx muscle during exercise is reduced relative to controls, as is the rate of pH recovery. Total lactate is not elevated in the cells and so it is argued that there is a reduction in the capacity to export proton equivalents in muscles of mdx mice which could be caused by an elevation in intracellular sodium. This provides more evidence of impaired ionic regulation in dystrophic muscle and could be used as an index for the evaluation in vivo of therapeutic interventions such as myoblast transfer or gene replacement therapy.     

Abnormal respiratory regulation in myotonic dystrophy]

The abnormal respiratory regulation as well as respiratory muscle degeneration are thought to be involved in the pathogenesis of alveolar hypoventilation in myotonic dystrophy (MD). In the present study we recorded changes in oxygen saturation resulting from exercise and hyperventilation in MD, Duchenne muscular dystrophy (DMD) patients and healthy volunteers by pulse oxymetry. Following are the results obtained in this study. (1) In DMD individuals showing preexisting mild desaturation around 90-95%, mild muscle exercise such as drawing a picture always caused further desaturation, which is presumably due to an increase in oxygen demand. On the other hand the MD patients with the same level of desaturation often showed paradoxical improvement in oxygen saturation up to 95-97% after a similar mild exercise, however, they showed obvious desaturation by a harder exercise such as propelling wheelchair. (2) There was a fluctuation of oxygen saturation at rest in MD, while this was not apparent in DMD patients and normal volunteers. (3) In MD and normal individuals, a strenuous hyperventilation is always followed by an oxygen desaturation through ventilatory suppression probably caused by hypocapnea resulting from the hyperventilation. This desaturation phase is much more prolonged in MD patients than in normal control subjects. The above data indicate further evidence of abnormal ventilatory regulation in MD.     

A study of the relationship between participation in common leisure activities and seizure occurrence

OBJECTIVE: To investigate whether participation in a structured programme of fairly intensive leisure activities increased seizure occurrence. MATERIAL AND METHODS: 212 adults with medically-intractable epilepsy were closely monitored for seizure occurrence during an "activities day", i.e. a day consisting of various structured sessions of leisure pursuits (video game play, reading, word puzzles, television, physical exercise), and during other days of relative rest, whilst undergoing prolonged video EEG monitoring. RESULTS: The relative risk of seizures did not differ significantly during activities days [0.71 (95% CL: 0.38 to 1.33)] compared with days of relative rest. CONCLUSIONS: These findings fail to provide empirical support for the hypothesis that cognitive exertion has an adverse effect on seizure control.     

Phosphorus nuclear magnetic resonance evidence of abnormal skeletal muscle metabolism in chronic alcoholics

Pathophysiologic events leading to rhabdomyolysis in alcoholics are not clearly understood. We examined 18 alcoholic patients (10 with and 8 without a recent history of rhabdomyolysis) and 15 healthy non-alcoholic volunteers by phosphorus nuclear magnetic resonance spectroscopy of thenar eminence muscle. At rest, phosphocreatine, ATP, and pH levels were similar in patients and control subjects. During aerobic exercise, phosphocreatine utilization was greater, pH fell more slowly, and maximum acidosis was less in alcoholics with previous rhabdomyolysis than in control subjects. During ischemic exercise, both patient groups exhibited a significantly slower and smaller decrease in pH than did control subjects. These findings are consistent with impaired muscular glycolysis or glycogenolysis in both alcoholic groups. This metabolic myopathy may contribute to the onset of acute rhabdomyolsis.     

Exercise performance and fatiguability in patients with chronic fatigue syndrome.

To examine the role of delay in recovery of peripheral muscle function following exercise in the fatigue experienced by patients with the chronic fatigue syndrome (CFS) and to examine the influence of effort perception in limiting exercise performance in these patients, a study was carried out on a group of twelve patients with chronic fatigue syndrome and 12 sex and age-matched sedentary control subjects. Symptom limited incremental cycle exercise tests including measurements of perceived exertion were performed followed by examination of the contractile properties of the quadriceps muscle group for up to 48 hours. Muscle function was assessed by percutaneous electrical stimulation and maximum voluntary contractions. Muscle function at rest and during recovery was normal in CFS patients as assessed by maximum isometric voluntary contraction, 20:50 Hz tetanic force ratio and maximum relaxation rate. Exercise duration and the relationship between heart rate and work rate during exercise were similar in both groups. CFS patients had higher perceived exertion scores in relation to heart rate during exercise representing a reduced effort sensation threshold of 3.2 units on an unmodified Borg scale in CFS patients. Patients with chronic fatigue syndrome show normal muscle physiology before and after exercise. Raised perceived exertion scores during exercise suggest that central factors are limiting exercise capacity in these patients.     

Ca2+-ATPase deficiency in a patient with an exertional muscle pain syndrome.

31P Magnetic resonance spectroscopy studies were carried out in vivo on skeletal muscle of a patient with verapamil-responsive, chronic, progressive post-exertional muscle pain. A sister suffered from a similar complaint. The results showed that the muscle: (1) decreased its high energy phosphate content more rapidly than normal during exercise, indicating either increased utilisation or decreased production of ATP; (2) acidified more rapidly than normal during exercise suggesting an increased glycolytic rate; (3) continued in some studies to acidify markedly during the first minute after exercise, indicating that glycolysis remained active into the recovery period; (4) had phosphocreatine and ADP recovery rates consistent with normal rates of oxidative phosphorylation. On the basis of these results, it was proposed that the patient suffers from a defect in Ca2+ handling in the muscle. Subsequently, direct measurement of Ca2+-ATPase activity in the sarcoplasmic reticulum fraction from a muscle biopsy sample showed that the activity of this enzyme was reduced by about 90%.     

Resting oxygen consumption and in vivo ADP are increased in myopathy due to complex I deficiency

BACKGROUND: Patients with isolated complex I deficiency (CID) in skeletal muscle mitochondria often present with exercise intolerance as their major clinical symptom. OBJECTIVE: To study the in vivo bioenergetics in patients with complex I deficiency in skeletal muscle mitochondria. METHODS: In vivo bioenergetics were studied in three of these patients by measuring oxygen uptake at rest and during maximal exercise, together with forearm ADP concentrations ([ADP]) at rest. Whole-body oxygen consumption at rest (VO(2)) was measured with respiratory calorimetry. Maximal oxygen uptake (VO(2)max) was measured during maximal exercise on a cycle ergometer. Resting [ADP] was estimated from in vivo (31)P MRS measurements of inorganic phosphate, phosphocreatine, and ATP content of forearm muscle. RESULTS: Resting VO(2) was significantly increased in all three patients: 128 +/- 14% (SD) of values in healthy control subjects. VO(2)max in patients was on average 2.8 times their VO(2) at rest and was only 28% of VO(2)max in control subjects. Resting [ADP] in forearm muscle was significantly increased compared with healthy control subjects (patients 26 +/- 2 microM, healthy controls 9 +/- 2 microM). CONCLUSION: In patients with CID, the increased whole-body oxygen consumption rate at rest reflects increased electron transport through the respiratory chain, driven by a decreased phosphorylation potential. The increased electron transport rate may compensate for the decreased efficiency of oxidative phosphorylation (phosphorylation potential).     

Forearm exercise increases plasma hypoxanthine.

Plasma hypoxanthine was measured in three normal subjects during aerobic forearm exercise. The comparative increase of hypoxanthine greatly exceeded that of ammonia or lactate. It is proposed that hypoxanthine production reflects ATP breakdown in muscle. The test may prove useful in the investigation of patients with metabolic muscle disease.     

Phosphorus magnetic resonance spectroscopy of partially blocked muscle glycolysis. An in vivo study of phosphoglycerate mutase deficiency

In vivo phosphorus magnetic resonance spectroscopy was used to evaluate the changes in muscle bioenergetics in a patient with a partial glycolytic block. Phosphoglycerate mutase-deficient muscle showed the following evidence: Abnormal accumulation of sugar phosphates does occur, even when 6% enzyme activity is present. The elimination of sugar phosphates was faster than in complete glycolytic blocks. Mild intracellular acidosis occurred during ischemic exercise. The energy state was slightly low at rest but not during exercise. Postexercise recovery was mildly slowed. These findings suggest that phosphorus magnetic resonance spectroscopy can detect partial defects, as well as full glycolytic blocks, in muscle metabolism.     

Adynamia episodica hereditaria: What causes the weakness?

The cause of weakness was investigated in a patient with adynamia episodica hereditaria without myotonia. A pattern of exercise and rest produced episodes of hyperkalemic periodic paralysis. In addition, local muscle weakness was induced by forearm cooling. Investigations on isolated intercostal muscle demonstrated that a high potassium concentration in the bathing solution triggered a noninactivating membrane current causing depolarization of the muscle fibers. This current was carried by sodium as it could be inhibited by tetrodotoxin. The abnormal sodium conductance led to an increase of sodium within the fibers. This was demonstrated directly by intracellular recordings. Weakness induced by rest after exercise and cold-induced weakness appeared to have different pathomechanisms. In the cold, the muscle fibers retained a normal resting potential, but their excitability was reduced and their mechanical threshold was increased. These findings also provide evidence that the mechanism of cold-induced weakness in adynamia episodica is distinctly different from the cold-induced weakness that occurs in paramyotonia congenita.