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J Thom

Publications and source records attributed to J Thom.

26 records · Page 2Linked to original sources
PubMed1995

Rapid detection of hereditary and acquired platelet storage pool deficiency by flow cytometry.

Platelet aggregation is commonly used to investigate patients with possible dense granule storage pool deficiency (delta SPD), but recent studies have shown that this investigation is not specific or sensitive for this disorder. We describe a simple one-step technique to detect mepacrine loaded platelets by flow cytometry and found a good correlation (r = 0.83) between this method and the enumeration of platelet dense granules by conventional fluorescent microscopy. Seven patients with congenital delta SPD had significantly (P < 0.001) reduced mepacrine labelling detected by flow cytometry (mean 15%; range 5-23%) compared to normal controls (mean 48%; normal range 32-64%). Six patients with other hereditary platelet disorders had normal mepacrine labelling (mean 49%; range 34-66%) and were clearly distinguished from patients with delta SPD despite similar platelet aggregation patterns. Acquired delta SPD is frequently associated with the platelet function defect described in the myeloproliferative and myelodysplastic disorders (MPD/MDS) and we compared platelet aggregation and mepacrine labelling in 15 of these patients. The results confirm that delta SPD occurs commonly in MPD/MDS with 7/15 patients having reduced mepacrine staining but, like the findings in hereditary delta SPD, 3/7 patients with normal platelet aggregation had delta SPD. Similarly abnormal platelet aggregation was not diagnostic of delta SPD as 4/8 of these patients had normal mepacrine levels. These results may contribute to the known lack of correlation between the limited assessment of platelet function and bleeding events in MPD/MDS. We found mepacrine labelling of platelets detected by flow cytometry to be a useful, simple and inexpensive method to detect hereditary and acquired delta SPD which will improve the definition of the platelet defect in these disorders in the clinical laboratory.

Adult↗
PubMed1990

Fluid production by in vitro lungs from fetal guinea pigs.

Lungs from fetal guinea pigs (54-67 days of gestation) were supported in vitro, and lung liquid secretion rates were measured by a dye-dilution technique. The average secretion rate in the first hour was 2.14 +/- 0.08 (SE) mL x kg-1 body weight.h-1 (0.21 +/- 0.01 mL/h) (n = 450); this was comparable to intact preparations. In an independent study of 30 lungs, secretion continued unchanged for 3 h, with no significant change in fluid composition. Between 54 days and term, production appeared to fall in terms of millilitres per kilogram per hour. The following agents were placed in the supporting saline during the middle hour of incubation. (i) Sodium iodoacetate: at 10(-4) M this produced a fall in secretion (fall, succeeding hours; 55.4 +/- 23.0 and 64.9 +/- 17.5%; n = 6); at 10(-3) M it stopped secretion (fall, succeeding hours; 87.2 +/- 10.3 and 100%, n = 6). (ii) Ouabain: at 10(-5) M there was no change in production (n = 6); at 10(-4) M, four preparations were unaffected, two reduced production. (iii) Epinephrine (10(-7) M) produced a significant fall in production in all cases (n = 6); in four preparations secretion reduced (average fall, 64.4 +/- 10.8%); in two preparations there was reabsorption (average rate, -1.03 mL.kg-1.h-1). This extends the effect of epinephrine to the guinea pig, and suggests that the in vitro preparation is a useful model for studies of the fetal lung.

Animals↗
PubMed1990

The effects of furosemide and bumetanide on lung liquid production by in vitro lungs from fetal guinea pigs.

Lungs from fetal guinea pigs of 61 +/- 3 days of gestation were supported in vitro for 3 h, and lung liquid secretion rates were measured by a dye dilution technique based on Blue Dextran 2000. Ten preparations that had received no treatment showed an average secretion rate of 1.12 +/- 0.28 mL.kg-1 body weight.h-1 during the first hour, and there were no significant changes over the following 2 h. In studies of 54 fetal lungs, furosemide, bumetanide, control ethanol carrier, or saline alone were placed in the supporting medium during the middle hour of the 3-h incubations (ABA design). Furosemide at 10(-3) M reduced secretion 83.4 +/- 16.8%; at 10(-4) and 10(-5) M it produced smaller reductions. Bumetanide at 10(-3) M usually produced reabsorption (129.9 +/- 23.0% reduction), at 10(-4) M it reduced secretion 30.9 +/- 11.8%, but at 10(-5) M it was ineffective. Control carrier and saline were without effect. The ability of the loop diuretics to produce reabsorption of fluid in some preparations suggests the unmasking of an active reabsorptive process. The results also suggest that lung liquid secretion in the fetal guinea pig, as in the sheep, is dependent on a Na+ and Cl- cotransport system.

Animals↗
PubMed1985

A signal sequence mutant defective in export of ribose-binding protein and a corresponding pseudorevertant isolated without imposed selection.

Ribose-binding protein is exported to the periplasmic compartment of Escherichia coli by a process that involves proteolytic cleavage of an amino-terminal extension of amino acids from the precursor form of the protein. In a collection of mutants isolated as defective in the Rbs transport system, a strain was identified that contained only precursor ribose-binding protein, none of which was exported to its normal location in the periplasm. The mutated rbsB contained a base substitution that results in a change of leucine to a proline at position-17 in the signal sequence. A pseudorevertant of the mutant contained proteolytically processed, active ribose-binding protein in the periplasm. The pseudorevertant rbsB carried a second mutation: serine at position-15 in the signal sequence was changed to phenylalanine. Isolation of a signal sequence mutant and a corresponding pseudorevertant without specific selection or site-directed mutagenesis emphasizes the possibility of obtaining export mutants without the use of procedures that could bias or limit the range of mutations found. Explanation of the extreme phenotype of the mutant and the effective correction of that phenotype in the pseudorevertant requires extension of current notions of critical features of signal sequences.

Amino Acid Sequence↗
PubMed1984

Intestinal absorption of thiamin in man compared with folate and pyridoxal and its subsequent urinary excretion.

off intestinal absorption of thiamin was compared with that of folate and pyridoxal in six healthy volunteers using an oral dose of each vitamin equivalent to ten times the recommended daily allowance. Folate and pyridoxal were rapidly absorbed and following the oral dose, serum concentrations rose from a mean basal level of 10.9 micrograms/liter and 17.5 micrograms/liter to 174.8 micrograms/liter and 315.2 micrograms/liter respectively--an increases of 1,500% for folate and 1,701% for pyridoxal. The mean serum level of thiamin rose only marginally from 5.1 micrograms/liter to 7.2 micrograms/liter, an increase of 42%. One hour following the oral test dose of thiamin, the vitamin was actively excreted in the urine of all volunteers, with a mean creatinine/thiamin renal clearance ratio of 2.4. Active excretion continued for up to six hours. In contrast, folate was only actively cleared for a short period in two volunteers. Thiamin absorption appeared to be controlled and limited, and modest increases in the serum concentration were accompanied by active renal clearance.

Administration, Oral↗
PubMed1983

A microbiological assay for the measurement of methotrexate in biological fluids.

A microbiological assay for the measurement of methotrexate has been designed, using a chloramphenicol resistant mutant of Lactobacillus casei as the test organism. The method is simple, precise and inexpensive. Results are not significantly different from those obtained using a methotrexate radioassay kit employing a competitive protein binding technique. However, where patients are being treated with co-trimoxazole, the competitive protein binding technique is unsuitable for measuring methotrexate levels due to the cross reactivity of the binder. This is not a problem with the microbiological assay described here, which is able to measure methotrexate in the presence of large doses of trimethoprim. The methods were not affected by the presence of seven commonly encountered antibiotics. These had negligible effect on either method up to concentrations of 100 mg/l.

Anti-Bacterial Agents↗