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Biomedical subjects

M J Thomas

Publications and source records attributed to M J Thomas.

At least 199 records · Page 11Linked to original sources
PubMed1981

A reappraisal of the free thyroxine index.

The usefulness of the routine measurement of the free thyroxine index as opposed to that of total thyroxine only has been examined by analysis of 803 requests for thyroid function tests in adults. In only 2.7% of cases would a significantly different decision on the interpretation and the need for supplementary testing have been made by considering the thyroxine result alone. These discrepancies could be readily avoided by using slightly wider limits for the performance of supplementary tests. It is concluded that the work and cost of the routine measurement of the free thyroxine index are not justified.

Binding Sites↗
PubMed1981

Release and metabolism of arachidonic acid in human neutrophils.

Dual radiolabel incorporation of [3H]arachidonic acid and [14C]palmitate or [14C]stearate by human neutrophils was employed to study both the release and metabolism of arachidonic acid. Results indicate the involvement of a phospholipase A2 mechanism causing [3H]arachidonate release from membrane phospholipid. Phosphatidylinositol and phosphatidylcholine were the sources of [3H]arachidonate; about twice as much radiolabeled phosphatidylinositol was degraded as phosphatidylcholine. Challenge of neutrophils with opsonized zymosan and calcium ionophores caused the release of [3H]arachidonate; however, ionophores but not opsonized zymosan led to the production of [3H]hydroxyicosatetraenoic acid and [3H]dihydroxyicosatetraenoic acid. These products were preferentially released by neutrophils into the extracellular milieu in contrast with free [3H]arachidonate which remained cell associated. One-third of the [3H]hydroxyicosatetraenoic acid but not [3H]dihydroxyicosatetraenoic acid was reincorporated into cellular lipid, primarily phospholipid. No significant production of [3H]prostaglandin or [3H]thromboxane was detected. In contrast to zymosan and ionophore, phorbol myristate acetate, another potent stimulant of neutrophil oxidative metabolism and degranulation, did not release [3H]arachidonate.

Arachidonic Acid↗
PubMed1981

Effect of phagocytosis and ionophores on release and metabolism of arachidonic acid from human neutrophils.

Challenge of human neutrophils prelabeled with [3H] arachidonate and [14C] palmitate or [14C]-stearate with opsonized zymosan or the Ca2+ ionophores A23187 or Ionomycin caused the release of [3H], but not [14C], fatty acid. With the ionophores, but not zymosan, considerable conversion of the [3H] arachidonate to hydroxyeicosatetraenoates occurred. Although various isomers were recovered, the 5-hydroxyeicosatetraenoate appeared to be the major product. In these experiments, no [14C] products were detected such as lysophospholipid, diglyceride or monoglyceride. Although no definite statement can be made about the mechanism of release of arachidonate, our data are most easily interpreted as the result of the action of a phospholipase A2.

Anti-Bacterial Agents↗
PubMed1981

Biliary stricture.

Comparison of our results for the past 14 years with those from the period 1940 through 1968 shows that surgical therapy in the repair of biliary stricture has plateaued at a consistent level of more than 90 per cent success. The selection of an operative procedure and its conduct have become standardized based on the principles discussed earlier. The patients that have an unsatisfactory outcome are for the most part predictable. They are mainly those with biliary cirrhosis and its complications, ineradicable intrahepatic stone formation, or rare injuries that are technically incorrectable. Current experience reinforces our previous observation that a history of one or more previous unsuccessful repairs does not preclude success after another attempt. More than 80 per cent of such patients have been rendered symptom-free by stricture repair (Table 3). Since surgical therapy eliminates the need for external tubes and the perpetual morbidity of other forms of palliative therapy, it remains the mainstay of treatment for all but a handful of patients.

Adult↗
PubMed1981

Neutrophil-degranulating action of 5,12-dihydroxy-6,8,10,14-eicosatetraenoic acid and 1-O-alkyl-2-O-acetyl-sn-glycero-3-phosphocholine. Comparison with other degranulating agents.

5,12-Dihydroxy-6,8,10,14-eicosatetraenoic acid was prepared from rabbit neutrophils challenged with ionophore A23187 plus arachidonic acid. It was purified by reverse-phase high-performance liquid chromatography with the use of a two-step procedure that effectively resolved the lipid from closely eluting contaminants. The phospholipid 1-O-alkyl-2-O-acetyl-sn-glycero-3-phosphocholine was prepared from beef heart plasmalogen. Confirming earlier reports, both lipids stimulated human polymorphonuclear neutrophils to release granule-bound enzymes. Their respective degranulating actions took less than 5 minutes to become maximal, were dependent upon the presence of cytochalasin B, and required intact pathways of arachidonic acid metabolism, as judged by the inhibitory actions of arachidonate antimetabolites. Neither lipid required more than trace concentrations of extracellular calcium to effect optimal amounts of enzyme release. In one or more of these regards the two lipids differed strikingly from other neutrophil-degranulating agents such as A23187, N-formyl-methionyl-leucyl-phenylalanine, and phorbol myristate acetate. The mechanism of action of the two lipid stimuli, therefore, appear to differ somewhat from the mechanisms of the other three stimuli.

Animals↗
PubMed1981

Radioimmunoassay for serum and urinary lysozyme.

We describe a radioimmunoassay for lysozyme (EC 3.2.1.17, mucopeptide N-acetylmuramohydrolase) in plasma and urine. It involves use of an antibody, raised in rabbits, to lysozyme from urine from a patient with monocytic leukemia. This antiserum, diluted 4000-fold, is incubated with radiolabeled lysozyme for 2 h and antibody-bound lysozyme is separated from free lysozyme with dextran-coated charcoal. Validation of the assay included precision and parallelism studies with serum and urine samples from patients with monocytic leukemia and analgesic nephropathy. Results of the radioimmunoassay and those obtained with a Micrococcus lysodeikticus lytic assay correlated well (r = 0.94). Sensitivity of the assay was 3.5 micrograms/L for both serum and urine. The main advantages of the assay are its good precision and reproducibility and its high sensitivity.

Humans↗
PubMed1981

Neutrophil-aggregating activity of monohydroxyeicosatetraenoic acids.

The following oxidative derivatives of arachidonic acid were prepared and assayed for their ability to aggregate cytochalasin-B-pretreated human neutrophils: 5-, 8-, 9-, 11-, 12-, and 15-hydroxyeicosatetraenoic acids. The compounds were prepared by oxidation of arachidonic acid and purified by direct and reverse phase high performance liquid chromatography. Each lipid was racemic at the hydroxy residue and had a cistrans conjugated double bond adjacent to the hydroxy residue. Except for racemization, therefore, they were identical to hydroxyeicosatetraenoic acids generated by neutrophils exposed to diverse aggregating stimuli. In addition, 15-L-hydroxyeicosatetraenoic acid was prepared from soybean lipoxygenase. Of these 7 fatty acid preparations, only 5- and 12-hydroxyeicosatetraenoic acid aggregated the cells. Thus, the bioactions of these lipids are crucially dependent upon the position of the hydroxy residue. The 5- and 12-hydroxy derivatives were potent aggregating agents, inducing half-maximal responses at 200 and 40 nM, respectively. Their bioactions required extracellular calcium and magnesium. And the response to both fatty acids was effectively blocked by three inhibitors of cellular arachidonic acid metabolism: nordihydroguaiaretic acid, 5,8,11,14-eicosatetraynoic acid, and indomethacin. The 5- and 12- hydroxyeicosatetraenoic acids, therefore, may induce neutrophils to metabolize their endogenous arachidonate. Alternatively, the two hydroxy acids themselves may be further metabolized through pathways inhibited by arachidonate antimetabolites into a final mediator(s) of aggregate formation.

12-Hydroxy-5,8,10,14-eicosatetraenoic Acid↗
PubMed1978

Measurement of serum ferritin by radioimmunoassay.

A direct radioimmunoassay for ferritin in serum is described in which Bolton and Hunter reagent is used to label ferritin. The detection limit of the assay is 150 pg; 95% reference ranges were found to be 12-200 microgram/l for men and 5-76 microgram/l for women. Ferritin concentrations in patients with iron deficiency anaemia were found to be uniformly low in subjects with uncomplicated iron deficiency but were normal or even raised in subjects with iron deficiency anaemia associated with malignant or inflammatory conditions.

Adolescent↗
PubMed1977

The detection and measurement of D-norgestrel in human milk using Sephadex LH 20 chromatography and radioimmunoassay.

An accurate sensitive method for the assay of D-norgestrel in human milk is described. The steroid is isolated from an ether extract of milk by Sephadex LH 20 chromatography in the system iso-octane-benzene-methanol (70:20:10 v/v). The radioimmunoassay utilises a specific antibody produced in rabbits against D-'norgestrel 3-(O-carboxymethyl) - oxime coupled to bovine serum albumin with D-norgestrel 3-(0-carboxymethyl) -oxime/ [125I]-iodohistamine conjugate as radioligand. Accuracy, sensitivity and blank value are satisfactory. Milk samples were obtained from three subjects treated with 30 microgram/day D-norgestrel, treatment commencing two weeks following parturition. Significant amounts of D-norgestrel were found, ranging between 92-135 pg/ml milk at the end of the first two-week treatment regimen. In two of three subjects, lower, but significant concentrations (53 pg and 35 pg/ml respectively) of steroid were found at the end of four weeks treatment. In the third subject, D-norgestrel could not be detected at this time. As a check on the specificity of the assay, three samples were submitted to additional chromatographic purification on alumina thin layer in the system benzene-cyclohexane-ethanol (70:27:3 v/v). Although this additional chromatographic step yielded somewhat lower values, agreement between the respective sets of results was good. The significance and implications of these findings are discussed.

Chromatography, Gel↗