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Biomedical subjects

D R Wilkie

Publications and source records attributed to D R Wilkie.

At least 19 recordsLinked to original sources
PubMed1995

The relationship between plasma urea levels and some muscle trimethylamine levels in Xenopus laevis: a 31P and 14N nuclear magnetic resonance study.

Urea is known to be disruptive to proteins, yet high levels occur in a variety of tissues. It has been suggested that trimethylamines counteract the effects of urea on protein. We have, therefore, directly investigated whether elevating tissue urea levels produces an increase in trimethylamine concentrations by using 31P and 14N nuclear magnetic resonance (NMR) spectroscopy to detect two trimethylamines (glycine betaine and glycerylphosphorylcholine) in intact, living gastrocnemius muscle from Xenopus laevis. Xenopus laevis naturally elevates its tissue urea levels under dry conditions. This ability was used to obtain plasma urea levels ranging from 1 to 110 mmol l-1. This procedure did not alter pH or levels of ATP or phosphocreatine in the muscles, but did raise trimethylamine levels. We find that there is a significant relationship between plasma urea concentrations and the trimethylamine levels studied. This relationship was, however, limited to the lower range of urea levels. We propose that other trimethylamines or mechanisms come into play at urea concentrations above 20 mmol l-1.

Animals↗
PubMed1991

Nuclear magnetic resonance studies of blood plasma and urine from subjects with chronic renal failure: identification of trimethylamine-N-oxide.

We have used 1H-, 13C- and 14N-NMR spectroscopy to investigate the constituents of plasma and urine in 16 patients with chronic renal failure (CRF). Resonances not previously observed in spectra of plasma from healthy volunteers were seen in CRF plasma, including those for trimethylamine-N-oxide (TMAO) and dimethylamine (DMA). A possible analogy with the plasma of elasmobranch fishes, in which TMAO stabilizes proteins in the presence of very high urea concentrations, is noted. The intensity of the TMAO resonance for CRF subjects was correlated with the plasma concentration of urea (R = 0.55) and creatinine (R = 0.74), suggesting that the presence of TMAO is closely related to the degree of renal failure. When normal subjects ate a meal of TMAO-containing fish, TMAO appeared rapidly in the plasma and in the urine. Thus TMAO is efficiently cleared by the healthy kidney. Differences in the interaction of lactate with plasma proteins were detected by NMR, suggesting that uraemia impairs their transport roles.

Adult↗
PubMed1986

Muscular fatigue: effects of hydrogen ions and inorganic phosphate.

During muscular fatigue two metabolites, hydrogen ions (H+) and inorganic phosphate (Pi), increase in concentration. The effect of increase in [H+] has been modeled mathematically for a system containing creatine kinase (EC 2.7.3.2), adenylate kinase (EC 2.7.4.3), and the appropriate concentrations of their substrates. Assuming that no other equilibrium reactions are involved, the result of acidification should be a useful increase in the ratio [ATP]/[ADP]. It is also shown by a reanalysis of earlier 31P NMR studies that the observed combination of increased [H+] and increased [Pi] leads to an increase in the monobasic phosphate concentration [Pi-] that is inversely proportional to the force of contraction. This suggests that Pi- may be a direct inhibitor of the actomyosin ATPase system.

Animals↗
PubMed1984

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.

Adenosine Diphosphate↗
PubMed1984

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.

Adenosine Triphosphate↗
PubMed1983

Non-invasive investigation of cerebral metabolism in newborn infants by phosphorus nuclear magnetic resonance spectroscopy.

Intracellular metabolism in the brains of seven infants, born at 33-40 weeks' gestation and aged 44 h to 17 days, was studied on fourteen occasions by phosphorus nuclear magnetic resonance spectroscopy (31P NMRS). The characteristic spectral peaks of ATP, phosphocreatine (PCr), phosphodiesters, and inorganic orthophosphate (Pi) were always detected, together with a large peak attributed mainly to ribose-5-phosphate. The ratio of PCr to Pi NMRS signals (which are related to concentration) in one infant thought to have a normal brain was 1.7. In three infants who had severe birth asphyxia the PCr/Pi ratio ranged from 0.2 to 1.0 but increased as their clinical condition improved: infusions of mannitol solution caused a rapid increase in the ratio on four occasions in two of these infants. The PCr/Pi ratio was 1.4 in an infant with congenital cerebral atrophy and 0.7 in an infant with meningitis. Grossly abnormal 31P spectra antedated the detection by ultrasound of large porencephalic cysts in two infants. No systematic changes in intracellular pH (calculated from the chemical shift of the Pi resonance) were observed: the mean value for all observations was 7.2 +/- SD 0.1 (n = 14).

Adenosine Triphosphate↗
PubMed1981

The activity of creatine kinase in frog skeletal muscle studied by saturation-transfer nuclear magnetic resonance.

1. The activity of creatine kinase in intact anaerobic frog muscle at 4 degrees C at rest and during contraction was investigated by using saturation-transfer 31P n.m.r. 2. At rest, the measured forward (phosphocreatine to ATP) reaction flux was 1.7 X 10(-3) M . s-1 and the backward flux was 1.2 X 10(-3) M . s-1. The large magnitude of both fluxes shows that creatine kinase is active in resting muscle, so the observed constancy of [phosphocreatine] demonstrates that the enzyme and its substrates are at equilibrium. 3. The apparent discrepancy between the fluxes must arise largely from an underestimation of the backward flux resulting from interaction of ATP with other systems, e.g. via adenylate kinase. For purposes of further calculation we have therefore adopted 1.6 X 10(-3) M . s-1 as an estimate of both fluxes. 4. During contraction, when the creatine kinase reaction is no longer at equilibrium, the net rate of phosphocreatine breakdown, estimated directly from the change in area of the inorganic phosphate peak, was 0.75 X 10(-3) M . s-1. Saturation transfer indicates that the forward reaction flux remains at approx. 1.6 X 10(-3) M . s-1 and the backward flux decreases to about 0.85 X 10(-3) M . s-1. 5. The activity of creatine kinase during contraction is large enough to account for the well-established observation that, during contraction, the concentration of ATP falls by less than 2-3%. The reaction catalysed by creatine kinase is driven forward during contraction by the large relative increase in the concentration of free ADP, which is more than doubled. 6. The observation that the forward flux does not increase during contraction and that the backward flux decreases can most simply be explained on the basis of competition of reactants for a limited amount of enzyme.

Adenosine Triphosphate↗
PubMed1980

Studies of the biochemistry of contracting and relaxing muscle by the use of 31P n.m.r. in conjunction with other techniques.

When n.m.r. is applied to suitable chosen biological problems it yields a wealth of fundamental information unmatched by any other technique. By means of 31P n.m.r. we have studied intact living muscle at rest, during contraction and during recovery from contraction. Phosphocreatine, ATP, inorganic phosphate, phosphorylated intermediaries of glycolysis, pH and the binding of Mg2+ to ATP are observed directly in the spectra. From the spectra can be calculated the concentration of free ADP, the free energy change of ATP hydrolysis, the production of lactic acid and the total ATP turnover. Changes in these quantities can thus be followed continuously in vivo and we have shown how they are related to the decline in force development and to the slowing of relaxation that occur during fatigue. Similar methods have been applied to study the control of glycolysis.

Adenine Nucleotides↗
PubMed1980

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.

Adenosine Diphosphate↗