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W J Thoma

Publications and source records attributed to W J Thoma.

15 recordsLinked to original sources
PubMed1992

Energy metabolism and contractile function after 15 beats of moderate myocardial ischemia.

Difficulties in studying myocardial metabolism with adequate time resolution have led to contradictory conclusions regarding the mechanisms causing contractile abnormalities during the early stages of ischemia. In acutely instrumented swine, we investigated whether abnormalities in subendocardial ATP, phosphocreatine, or lactate content develop rapidly enough during the first few heart beats after onset of partial myocardial ischemia to contribute to contractile failure. Within the first 15 beats of a 40-50% reduction in left anterior descending coronary artery blood flow, regional myocardial function was significantly reduced but continuing to deteriorate. Rapidly frozen transmural left ventricular biopsies obtained on the 15th heart beat (+/- 1.5 beats) after the onset of ischemia revealed significant decrements in subendocardial phosphocreatine and ATP levels to 77% (p less than 0.05) and 84% (p less than 0.005) of control values, respectively, but minimal change in lactate content. Metabolic effects as assessed by transmural averages took longer to become detectable; thus, there was a tendency to underestimate the importance of subendocardial metabolic effects on myocardial function. When left ventricular preload was assessed during this early time period, left ventricular end-diastolic wall thickness only decreased by 3%, and left ventricular end-diastolic pressure did not change significantly despite a large fall in coronary perfusion pressure. Thus, in an in vivo pig model with techniques optimized to detect subendocardial metabolic changes within the period of very early moderate myocardial ischemia, abnormalities in high energy phosphate compounds occurred rapidly enough to contribute to developing myocardial dysfunction, whereas preload-mediated mechanisms related to vascular distending pressure could not explain the functional deterioration under these conditions.

Adenosine Triphosphate↗
PubMed1990

Regulation of the oxidative phosphorylation rate in the intact cell.

The mechanisms that underlie the balance between the consumption and oxidative generation of ATP in the intact cell are not well-defined. Cytosolic inorganic phosphate (Pi) and ADP levels, the cytosolic ATP/ADP ratio, and the cytosolic phosphorylation potential (PP) have all been proposed as major regulatory variables, the latter as a component of a "near-equilibrium" thermodynamic regulatory scheme. Therefore, the potential regulatory roles of these variables in the intact cell were evaluated with 31P NMR and Langendorff perfused rat hearts; in this preparation, the tissue oxygen consumption rate (MVO2) can be varied over a wide range. When the exogenous carbon source was varied, none of the proposed regulatory parameters, i.e., the ATP/ADP ratio, PP, or cytosolic ADP level, were found to be uniquely related to MVO2. Rather, ADP levels at a given MVO2 decreased progressively for the exogenous carbon sources in the following order: glucose, glucose + insulin, palmitate + glucose, lactate, pyruvate + glucose, and octanoate + glucose. In the octanoate and pyruvate groups, MVO2(-1) was linearly dependent upon [ADP]-1 with apparent Km values being in the range previously observed in isolated mitochondria. A similar trend was observed in the MVO2-[Pi] relationship. The present findings suggest that exogenous carbon sources which effectuate deregulation of intramitochondrial NADH generation lower cytosolic ADP and Pi to levels which are limiting to the rate of oxidative phosphorylation. For other carbon sources, the processes controlling the rate of NADH generation also participate in determining the rate of oxidative ATP synthesis. However, this control must be exerted kinetically rather than through a near-equilibrium thermodynamic mechanism as indicated by the present data and prior kinetic studies of the ATP synthetic process in both isolated mitochondria and intact myocardium [La Noue, K. F., et al. (1986) Biochemistry 25, 7667-7675; Kingsley-Hickman, P., et al. (1987) Biochemistry 26, 7501-7510].

Adenosine Triphosphate↗
PubMed1989

Injury and recovery of the liver from preservation assessed by 31P NMR spectroscopy: the contrast between preservation with Collins' solution and Ringer's lactate solution.

The biochemistry of hepatic injury and recovery from preservation for transplantation was studied in rat liver perfused in vitro with erythrocytes. ATP and its metabolites, inorganic phosphate (Pi) and pH were quantitated as often as every 2.5 min by 31P NMR spectroscopy during preservation and recovery. Release of the hepatocellular enzymes, lactate dehydrogenase V (LDV) and aspartate aminotransferase (AST) were also measured. The duration of preservation with Collins' solution, the standard clinical preservative, affected the rate of recovery of ATP and monophosphate esters (MP), which include AMP + IMP, and the final recovery of Pi, but not of ATP. The difference between Collins' and Ringer's lactate solution, a poor preservative, became more apparent as preservation time increased. The differences included (1) pH at the end of preservative infusion; (2) pH between 0 and 2.5 min of reperfusion; (3) the MP increase (AMP + IMP) at the end of 13 h of preservation; (4) rate of recovery of ATP after preservation; (5) final ATP recovery during reperfusion; (6) LDV after 13h of preservation. These biochemical differences between good and poor preservation form a rational basis for prediction of liver failure after transplantation and for tests of the quality of new preservatives.

Animals↗
PubMed1989

In vivo T1 values of phosphorus metabolites in human liver and muscle determined at 1.5 T by chemical shift imaging.

A procedure for obtaining T1 values for phosphorous metabolites in localized regions of human subjects, using a standard 1.5 T MR imager, is described. 31P spectra and T1 values localized to the liver, and to abdominal and calf muscle of healthy volunteers were obtained by means of a multi-slice spectroscopy technique, consisting of a chemical shift imaging (CSI) sequence with a B1-insensitive excitation and one dimension of phase encoding, used in conjunction with a surface coil. An examination consisting of proton imaging, shimming and collection of 31P progressive saturation spectroscopic data for T1 determination required 1 h to perform. Shimming on the signal from the body region detected by the surface coil gave spectra of excellent spectral resolution. Quantification of all peaks in the localized 31P spectra was carried out with the PIQABLE algorithm, and T1 values were calculated for inorganic phosphate (Pi), the phosphodiester region, and the ATP alpha-, beta- and gamma peaks of liver, and for calf muscle Pi, phosphocreatine (PCr), and the three ATP peaks. The precisions of the measurement and of the entire process for obtaining and quantifying localized spectra by one-dimensional CSI were determined, and the accuracy of T1 values obtained by this means was verified. The temporal variation in T1 values obtained in a series of examinations of a single normal subject was also assessed. The consistency of the T1 values obtained in this study with in vivo T1 values obtained by other techniques is a stringent test of accuracy of localized spectra obtained with CSI.

Adenosine Triphosphate↗
PubMed1989

Effect of adenine on liver nucleotide after fructose loading by 31P-NMR.

Livers from 125- to 150-g rats were perfused and the effect of fructose metabolism on liver energetics was observed using 31P nuclear magnetic resonance (NMR). Livers were exposed to fructose in a nonrecirculating manner for approximately 15 min and monitored for recovery for 30 min. At concentrations ranging from 1 to 25 mM, fructose exposure led to depletion of the nucleoside triphosphate level. Subsequently, the nucleoside triphosphate level recovered fully at a fructose concentration of 1 mM; however, recovery was only 65% of the initial values if the fructose concentration was 10 mM and 55% if the concentration was 25 mM. Adenine was found to protect nucleoside triphosphate levels against the adverse effects of fructose by blocking the deamination of AMP. In the presence of adenine, AMP accumulation was observed in the NMR spectra upon exposure of the liver to fructose.

Adenine↗
PubMed1988

Rapid 31P NMR test of liver function.

The 31P NMR spectrum of perfused rat liver was found to be dependent on the exogenous carbon available to the tissue. When pyruvate was supplied to liver initially perfused with lactate, Pi decreased, phosphoenol pyruvate and phosphomonoesters increased, and nucleotide pools remained the same. It is proposed that these changes can be used to evaluate liver function.

Animals↗
PubMed1988

pH and compartmentation of isolated perfused rat liver studied by 31P and 19F NMR.

The phosphorus NMR spectra of isolated perfused rat liver displays a prominent inorganic phosphate peak at 2.76 +/- 0.05 ppm relative to liver glycerolphosphocholine at 0.49 ppm. From titration curves of phosphorus-containing compounds this corresponds to a pH of 7.4. The spectra also display a shoulder on the prominent inorganic phosphate peak at 2.22 +/- 0.55 ppm corresponding to a pH of 7.0. Fructose is phosphorylated in the C1 position by the liver and the resulting fructose-1-phosphate is located in the cytosol. From the titration curves, this compound was at pH 7.0. When inorganic phosphate was added to the perfusate, 13 of 25 livers showed two inorganic phosphate peaks resolved in the difference spectra, one originating from the perfusate, the other at pH 7.0. When large (50 mM) fructose doses were administered to the liver, the prominent peak decreased allowing two peaks to be resolved. FCCP treatment of the liver caused the two peaks to coalesce with the final pH of both the fructose-1-phosphate and inorganic phosphate being the same. 19F NMR of difluoromethylalanine gave an intracellular pH of 7.4 for the isolated perfused liver. The data presented do not lend themselves to satisfactory interpretation, and call into question the correctness of the traditional assignment of liver inorganic phosphate being cytosolic in origin.

Animals↗
PubMed1988

31P nuclear magnetic resonance studies of effects of some chlorophenols on Escherichia coli and a pentachlorophenol-degrading bacterium.

A Flavobacterium sp. that mineralizes pentachlorophenol degrades some, but not all, of the other chlorinated phenols. Whole-cell 31P nuclear magnetic resonance was used to compare and observe transmembrane pH gradients and nucleotide pools in the Flavobacterium sp. and Escherichia coli after pentachlorophenol and 3,4,5-trichlorophenol were added to the cell suspensions. The data suggest that those chlorinated phenols which are not degraded by the Flavobacterium sp. may be resistant to degradation because they act as proton dissipators.

Biotransformation↗
PubMed1987

Saturation-transfer studies of ATP-Pi exchange in isolated perfused rat liver.

The rate of exchange between inorganic phosphate and ATP was measured in isolated perfused rat livers in the direction of ATP synthesis using 31P NMR spectroscopy and the saturation-transfer technique. Measurement of ATP hydrolysis was not observable, even after treatment of rats with 100 micrograms T3/day per 100 g body wt. When the perfused livers were treated with iodoacetate in order to inhibit glycolysis, NMR measurable exchange between ATP and Pi was eliminated. It is concluded that the inorganic phosphate----ATP conversion detected by saturation transfer is catalyzed by enzymes of the glycolytic pathway and that the mitochondrial ATPase rate is too slow to contribute to the observed effect.

Adenosine Triphosphate↗
PubMed1986

pH measurements by 31p NMR in bacterial suspensions using phenyl phosphonate as a probe.

Phenylphosphonate was used as an internal reference for 31p NMR measurements of E. coli cytoplasmic pH. Phenylphosphonate diffused into the cells allowing determination of pH, independent of magnetic susceptibility differences between intercellular and extracellular pools. Phenylphosphonate was used to measure pH changes during succinate uptake and metabolism, as well as during uncoupling of the transmembrane pH gradient by pentachlorophenol.

Diphosphates↗
PubMed1984

Effect of vitamin C deficiency on hydroxylation of trimethylaminobutyrate to carnitine in the guinea pig.

The effect of ascorbate deficiency on carnitine biosynthesis was investigated in young male guinea pigs. Liver and skeletal muscle carnitine levels were reduced in scorbutic animals. Heart and kidney concentrations remained unchanged. 14C-labeled 4-N-trimethylaminobutyrate was administered to control, pair-fed and scorbutic animals and distribution of isotope in compound present in the liver after 30 min was determined. Control and pair-fed animals converted trimethylaminobutyrate to carnitine faster than scorbutic animals. Injection of ascorbate with the [14C]trimethylaminobutyrate reversed the decline in trimethylaminobutyrate hydroxylase (EC 1.14.11.1) activity in scorbutic animals.

Animals↗