D.R. Wilkie

Mechanical relaxation rate and metabolism studied in fatiguing muscle by phosphorus nuclear magnetic resonance.

1. We have used phosphorus nuclear magnetic resonance (31P NMR) to study muscular fatigue in anaerobic amphibian muscle. In this paper the biochemical and energetic changes that result from a series of tetani are related to the decrease in rate constant (1/tau) for the final, exponential, phase of relaxation. 2. Using 31P NMR we have measured the concentrations of phosphocreatine (PCr), inorganic phosphate (Pi) and ATP as well as the internal pH. From our measurements we have calculated [creatine], [free ADP], the free‐energy change (more precisely, the affinity A = ‐dG/d xi) for ATP hydrolysis and the rates of lactic acid production and of ATP hydrolysis. 3. We have found that 1/tau, the rate constant of relaxation, is correlated with each of the following, independently of the pattern of stimulation: isometric force production, all of the measured or calculated metabolite levels, pH and dG/d xi. 4. There is a clear dependence upon the pattern of stimulation of the relation between 1/tau and each of the following: total duration of the experiment, number of contractions, rate of lactic acid production and rate of ATP hydrolysis. 5. The rate of relaxation is linearly related to [PCr], [creatine], [Pi] and dG/d xi. It is nonlinearly related to isometric force, [ATP], [H+] and rate of ATP hydrolysis. 6. We conclude that the change in 1/tau, like that of isometric force, depends upon metabolic factors, and not upon any independent changes in the activation or deactivation of contraction. We suggest that 1/tau may depend upon the free‐energy change for ATP hydrolysis which in turn may be related to the rate of Ca2+ uptake into the sarcoplasmic reticulum.

CEREBRAL ENERGY METABOLISM STUDIED WITH PHOSPHORUS NMR SPECTROSCOPY IN NORMAL AND BIRTH-ASPHYXIATED INFANTS

Phosphorus (31P) nuclear magnetic resonance spectroscopy was used to study intracellular metabolism in the brains of 6 normal newborn infants and 10 infants who had been asphyxiated during delivery. In the normal infants spectral peaks mainly attributable to adenosine triphosphate, phosphocreatine (PCr), phosphodiesters plus phospholipids, and inorganic orthophosphate (Pi) were always detected, together with an additional large peak in the phosphomonoester region indicating the presence of a metabolite or metabolites (probably largely phosphoethanolamine) which may be involved in rapid growth of the brain. In the asphyxiated infants, data obtained on the first day of life showed no differences from those in normal infants, but by the second to ninth days inverse changes in the concentrations of PCr and Pi had caused a significant reduction in PCr/Pi. This latency suggest the possibility of effective early treatment before irreversible metabolic damage sets in. Mean intracellular pH when PCr/Pi was minimal was 7.17 +/- 0.10. Values for PCr/Pi below 0.80 were associated with a very bad prognosis for survival and early neuro-developmental outcome.

Contraction and recovery of living muscles studied by 31p nuclear magnetic resonance

1. Phosphorus nuclear magnetic resonance (31P NMR) can be used to measure the concentrations of phosphorus‐containing metabolites within living tissue. We have developed methods for maintaining muscles in physiological condition, stimulating them and recording tension while at the same time accumulating their 31P NMR spectra. Experiments were performed on frog sartorii and frog and toad gastrocnemii at 4° C.

CLINICAL USE OF NUCLEAR MAGNETIC RESONANCE IN THE INVESTIGATION OF MYOPATHY

Abstract Topical nuclear magnetic resonance allows non-invasive investigation of the metabolism of skeletal muscle and other tissues. Energy exchange can be followed by measurement of 31 P NMR spectra which characterise changes in muscle content of inorganic phosphorus (Pi) and phosphorylcreatine. Muscle pH is determined from the chemical shift of Pi with respect to phosphorylcreatine. Topical NMR can be used to study changes in intermediary metabolites during exercise, and the clinical value is illustrated in a patient with phosphofructokinase deficiency who would otherwise have required multiple biopsies of muscle. In diseases such as Duchenne muscular dystrophy, where muscle may be partly replaced by fat or other tissue, the findings with 31 P NMR can be related to independent estimates of tissue composition obtained from 1 H and 13 C NMR spectra and from X-ray computerised tomography.

31P NMR Studies of Resting Muscle in Normal Human Subjects

Study of human tissues using 31P topical Magnetic Resonance is completely atraumatic; it allows simultaneous measurement of the concentrations of many important metabolites and of intracellular pH. In some critical situations, TMR yields more accurate results than those obtained by chemical analysis of tissue biopsies. We have shown that TMR can be calibrated to obtain quantitative measurements in human subjects. We have also shown that theories of control of glycolysis based on regulation by key metabolites of rate-limiting enzymes are inconsistent with the observed changes in intact muscle.

Cerebral metabolism in newborn infants studied by phosphorus nuclear magnetic resonance spectroscopy.

Publisher Summary This chapter discusses a study to examine the cerebral metabolism in newborn infants by phosphorus nuclear magnetic resonance spectroscopy. Six normal infants were studied. They were born at 28–40 weeks of gestation and NMR spectra were obtained when they were 16 h to 97 days old: their gestational-equivalent age at this time was 38–42 weeks. Unilateral lesions were detected by ultrasound in four infants born at 34–40 weeks of gestation and aged 1–14 days. In three of them the diagnosis was thought to be early cerebral infarction, and in the fourth, a small hemorrhage into a possibly infarcted area. PCr/Pi was always reduced in the affected hemisphere compared with the normal one. Depletion was far worse than encountered in any of the birth asphyxiated babies, and was accompanied by a profound intracellular acidosis. The infants subsequently died but there was no reason to suppose that the oxygen supply to the brain was seriously inadequate at the time when the studies were done. The metabolic abnormalities in both these illnesses inhibit the tricarboxylic acid cycle. The most likely explanation for the extremely severe disruption of energy status is that insufficient substrate was available for oxidative phosphorylation to occur.

Nuclear magnetic resonance spectroscopy in research and clinical diagnosis

A workshop on nuclear magnetic resonance (NMR) spectroscopy was held during the 17th Annual Scientific Meeting of the European Society of Clinical Investigation at Travemunde, West Germany, in April 1983. This was a timely review of the state of the art in a rapidly developing and exciting field which has considerable implications for clinical research. The first thing to establish is that NMR spectroscopy is different from the NMR imaging technique which has already proved to be of value in the few centres where this expensive new facility is available. Both forms of NMR depend on powerful magnet systems, but while the imaging methods employed at present make use of the magnetic characteristics of protons in water to produce a two-dimensional map similar to that obtained by X-rays, the great potential of NMR spectroscopy is the ability to determine, non-invasively, the concentrations of compounds containing such nuclei as 3’phosphorus, I3carbon and 19fluorine in selected volumes of human tissue. At last, we truly have a ‘magnetic eye on metabolism’ [I]. The fundamentals. of biological NMR were described by D.R. Wilkie who has played a large part in developing NMR spectroscopy as a tool for studying metabolism in muscle and brain. Atomic nuclei all possess charge and mass; some possess the quality of spin and this enables them to act as small ‘magnets’ and thereby be capable of responding to a magnetic field. Under the influence of a strong unidirectional magnetic field these nuclear magnets align themselves in a particular orientation. A perturbing radiofrequency signal at right angles will change the orientation of the nuclei, which, on cessation of this perturbing influence, return to their original distribution and emit energy. This process is detected by a radiofrequency receiver, and computer analysis of the detected signal yields a spectrum which has individual peaks as a result of differences in the immediate molecular environment around the individual nuclei. 3’P NMR is of particular value since compounds containing this atomic nucleus are so important in intracellular energy exchanges throughout all biological systems. The separation due to molecular structure