Biomedical subjects

D Foxall

Publications and source records attributed to D Foxall.

3 recordsLinked to original sources

PubMed2001

FAST sequences optimization for contrast media pharmacokinetic quantification in tissue.

The purpose of this study was to investigate the influence of the fast gradient-recalled echo (GRE) sequence parameters on the contrast dynamic range and signal sensitivity, to optimize the magnetic resonance (MR) sequence for contrast media pharmacokinetic assessment. Effects of the fast low-angle shot (FLASH), Fast acquisition at steady rate (FAST), and radiofrequency-spoiled (RF)-FAST sequence parameters were studied in vitro. The FAST sequence had the highest sensitivity in low gadolinium (Gd) concentration. The FLASH and RF-FAST sequences had a larger contrast dynamic range, but the FLASH images contained side band artifacts. Increasing the flip angle to 90 degrees raised the sensitivity of the FAST sequence and the contrast dynamic range of the RF-FAST sequence. The shortest possible TE was optimal for both contrast dynamics and imaging time. TI had an influence on the sensitivity of the FAST sequence only for small acquisition matrices. This study indicates the optimal parameters for contrast dynamics (RF-FAST, 90 degrees flip angle, shortest possible TE) and sensitivity (FAST, 90 degrees flip angle, long TI(eff)).

Contrast Media↗

PubMed1986

Nuclear magnetic resonance studies of carbohydrate metabolism and substrate cycling in Fasciola hepatica.

We have been interested in clarifying unique features of glycolytic metabolism in parasitic trematodes and in developing improved methods for monitoring the effects of pharmacologic agents that may alter functions of the pathway. In the present study metabolism of [1-13C]glucose by the common liver fluke, Fasciola hepatica, was studied both directly with 13C NMR and indirectly by observation of 13C-induced multiplet splitting of the 1H NMR resonances from the glycolytic end-products propionate and acetate. The extent of 13C enrichment of the end-products demonstrated that exogenous glucose was the predominant source of glycolytic substrate under the incubation conditions used. Specific enrichments of propionate and acetate in 13C were similar and enrichments at the acetate C-1 carboxyl and C-2 methyl were identical, demonstrating that acetate is generated preferentially from pyruvate formed by the malic enzyme reaction. End-product synthesized in substrate-free medium following incorporation of a small fraction of [1-13C]glucose into endogenous glycogen demonstrates that glucose equivalents from the most recently synthesized polymeric chains, which have a specific activity in 13C equal to that of the exogenous glucose, are preferentially used for glycogenolysis. Stimulation of flukes with 0.1 mM serotonin results in a reduction of the propionate/acetate 13C enrichment ratio consistent with functional "compartmentation" of glycogen pools having different structures and/or specific enrichment in 13C. Glucose equivalents were incorporated into glycogen in intact flukes with label at both the C-1 and C-6 positions during perfusion with [1-13C]glucose as a consequence of "substrate cycling" at the phosphofructokinase/fructosebisphosphatase enzyme couple. The observed glycogen C-6/C-1 labeling ratio of 0.42 and the net glycolytic flux of 11 mumol/g wet weight/hr imply a total forward flux of about 29 mumol/g wet weight/hr through phosphofructokinase with a reverse flux of about 17 mumol/g wet weight/hr through fructosebisphosphatase. Net glycolytic flux is therefore a poor estimate of the true flux through phosphofructokinase in this preparation.

Acetates↗

PubMed1985

31P-NMR studies of metabolite compartmentation in Fasciola hepatica.

Fasciola hepatica, the common liver fluke, is an anaerobic parasitic worm. Possible compartmentation of metabolites between different cell types, metabolic compartments, and free and macromolecule-bound species was investigated using 31P-NMR. A spectrum of the intact worm shows unusual metabolic features, among which are large amounts of glycerolphosphorylcholine, phospholipids mobile on the NMR time-scale, and free cytosolic ADP. Spectra from cells as different as those in oral sucker tissue and eggs showed similar features. Acidosis after serotonin administration was associated with parallel changes in chemical shifts of intracellular Pi and glucose 6-phosphate, suggesting that they are in the same metabolic compartment. Although 13.4 +/- 1.1 mumol/g wet wt. (n = 3) Mg2+ is present in fluke tissue, a considerable fraction is sequestered out of the cytosol. The intracellular free [Mg2+] was independently estimated from the chemical shifts of ATP and ADP as 1.6 +/- 0.5 mM and 2.9 +/- 0.7 mM, respectively. Quantitation of observable phosphate-containing metabolites in whole tissue and in perchlorate extracts demonstrated that 60% of the total ADP and 50% of the total Pi are 'NMR-invisible' in the intact fluke and therefore probably bound to macromolecules in the cells. The apparent ATP/ADP X Pi free concentration ratio is much lower in this anaerobic tissue than in mammalian oxidative tissues.

Adenosine Diphosphate↗