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Biomedical subjects

J Landon

Publications and source records attributed to J Landon.

At least 127 records · Page 7Linked to original sources
PubMed1977

Estimation of serum gentamicin by quenching fluoroimmunoassay.

A new type of non-isotopic immunoassay, applied to the determination of serum gentamicin, is reported. The method is based on partial quenching of fluorescence observed when fluorescein-labelled gentamicin is bound by anti-gentamicin serum. The fluorescence intensity of the labelled gentamicin in an unseparated immunoassay incubation mixture therefore serves to indicate the extent of binding, which is related to the amount of competing unlabelled gentamicin present. Precision and accuracy are shown to be similar to those of the best existing methods for gentamicin, while the new assay is more rapid and technically simpler, and avoids the use of expensive radio-chemicals with their attendant health hazard. Assays of patient samples correlate with established bioassay and polarisation fluoroimmunoassay methods.

Evaluation Studies as Topic↗
PubMed1977

Development of a highly sensitive radioimmunoassay for digoxin and its application in pediatric practice.

The sensitivity of two established routine digoxin radioimmunoassay methods has been increased to enable the provision of a rapid and relatively atraumatic inpatient and outpatient service for neonates and small children, using capillary blood samples obtained by heel-prick. The methods employ 125I- or 3H-labelled digoxin, a rabbit antiserum raised against a digoxin: bovine serum albumin conjugate and only 10 or 25 microliter of plasma as the sample. The results obtained using these highly sensitive assays correlate closely with those found using conventional assays, requiring larger sample volumes. An apparent difference in sensitivity to digoxin has been demonstrated between infants and children more than 1 yr old. Thus infants appear to tolerate plateau phase plasma levels (mean value for non toxic infants 2.6 +/- 1.8 ng/ml) that in older children or adults would be associated with digoxin toxicity.

Binding Sites, Antibody↗
PubMed1977

Radioimmunoassay for digoxin with a fully automated continuous-flow system.

We describe a fully automated continuous-flow radioimmunoassay for digoxin with use of a Technicon AutoAnalyzer system. It makes use of antibodies linked to magnetizable particles; a magnet separates the bound and free fractions. The precise dispensing of reagents by the AutoAnalyzer system permits a small incubation volume (about 160 microliter) and the reproducible timing enables non-equilibrium conditions to be used. Thus a single sample is assayed in 15 min, with a sample throughput of 30/h. The standard curve ranges from 0.5 to 8.0 microgram/liter and is most precise between 1 and 3 microgram/liter, the between-assay coefficient of variation being less than 3%. There is no significant carryover between samples of high and low concentration, and results by the method correlate closely (r = 0.969) with those by an established manual assay in which charcoal separation is used.

Antibody Specificity↗
PubMed1976

Polarisation fluoroimmunoassay of gentamicin.

A polarisation fluoroimmunoassay has been developed for the routine determination of gentamicin levels in serum. The method employs fluorescein-labelled gentamicin which is easily, reproducibly and economically prepared and has excellent shelf-life. The assay is fast (minimum incubation time 2 min) and requires 1.25 mul of serum. There is no separation step prior to readout of results. Recovery experiments reveal no serum effects. Intra- and inter-assay coefficients of variation are of the order of 10% or less. Estimations of gentamicin levels in patient serum samples correlate closely with those obtained by bioassay (r = 0.93) and radioimmunoassy (r = 0.97).

Biological Assay↗
PubMed1976

Solid-phase, magnetic particle radioimmunoassay.

A solid-phase radioimmunoassay system has been developed based on the use of antibodies covalently linked to polymer-coated iron oxide (EnzacrylR). An electro-magnet is employed both to mix the particles during incubation (by switching the field on and off) and to separate the antibody-bound and free fractions. This obviates the need for vertical rotation and for the time-consuming, multiple centrifugations required with conventional solid phase procedures. The system is universally applicable and methods have been established for the assay of thyroxine, human placental lactogen and digoxin. The thyroxine assay was employed as a model and it was shown that the results obtained for serum samples correlated closely with those using a routine liquid-phase radioimmunoassay. The applicability of employing a second antibody linked to the iron oxide particles was also studied.

Binding Sites, Antibody↗
PubMed1976

Introduction of a rapid, simple radioimmunoassay and quality control scheme for thyroxine.

A simple radioimmunoassay has been developed for service purposes to determine serum total thyroxine levels. Only three additions are required, of standard or sample, labelled thyroxine and antibody in polyethylene glycol. After 2 hours' incubation at room temperature the antibody-bound and free fractions are separated by centrifugation. Serum total thyroxine levels were measured in 195 euthyroid subjects and it was established that normal values lay within the range 57 to 155 nmol/1. Serial blood samples taken over a 24-hour period, from 11 subjects, indicated that there was no circadian rhythm so that samples for total thyroxine assay can be taken at any time of the day. Similar results were obtained using serum or plasma. Satisfactory results were obtained for three quality control sera when measured by seven different laboratories using this method.

Adolescent↗
PubMed1976

Chemical characterization of ectopic ACTH purified from a malignant thymic carcinoid tumor.

ACTH was purified from thymic tumor associated with ectopic ACTH production by gel filtration and ion exchange chromatography. Amino acid composition and C- and N-terminal analyses indicated that this tumor ACTH was comprised of the 2-38 sequence of authentic pituitary ACTH. The observations suggest that the mode of cleavage of this tumor ACTH from its precursor is different from that of pituitary ACTH.

Adrenocorticotropic Hormone↗
PubMed1975

The monocystic ovary syndrome.

Three patients with oligomenorrhoea and hirsutism thought to have the polycystic ovary syndrome were found to have only one ovarian cyst. Endocrine findings were similar to those found in the polycystic syndrome, but apart from the single cyst the ovaries were histologically normal; a biopsy specimen of a cyst showed normal follicular appearances and no evidence of luteinisation. These cysts may be the cause of this condition, producing abnormal amounts of ovarian steroids which modify the pituitary response. Further studies are needed, however, to determine this possibility.

Adult↗
PubMed1975

The measurement of urinary digoxin and dihydrodigoxin by radioimmunoassay and by mass spectroscopy.

A radioimmunoassay for urinary digoxin is described which includes an initial solvent extraction to remove factors in urine which cause non-specific interference in the assay. The recoveries obtained using different solvents are compared and the non-specific factors influencing the assay investigated further. These effects were overcome by the use of a small urine volume (10 mul) in a direct, unextracted, urine assay and the results obtained correlated closely with those from the assay using prior extraction (r=0.99). No false positive results were obtained with unextracted urine samples from hospitalised patients not receiving digoxin. The specificity was also determined with regard to the natural steroids, spironolactone and the metabolites of digoxin including dihydrodigoxin. The metabolite dihydrodigoxin, with a saturated lactone ring, was not detected whereas the mono-, and bis-digitoxo-sides and digoxigenin metabolites did cross react in the assay. It was not possible to separate dihydrodigoxin and digoxin by thin-layer chromatography or solvent extraction due to their similar structures, however, mass spectroscopy was successful in this respect and was employed to obtain the ratio of dihydrodigoxin to digoxin in extracted urine samples. Levels of urinary digoxin excreted by patients maintained on different oral doses of the drug were measured. The percentage excreted in the urine as digoxin correlated closely with the oral dose (r = 0.96) but was found to be lower than that reported in most previous studies. Mass spectroscopy measurements showed that an average of 16.4% (range 12.2-19.7%) of the total oral dose was excreted as dihydrodigoxin in the urine of nine patients investigated.

Animals↗
PubMed1975

The development of radioimmunoassays for fibrinogen degradation products: fragments D and E.

Fibrinogen degradation products, fragment D (FgD) and fragment E (FgE) have been measured in human serum by specific radioimmunoassays. In addition, the appearance of a neoantigenic determinant on FgD, revealed when fibrinogen is degraded by plasmin has been utilized to develop a specific radioimmunoassay for FgD in plasma (FgDneo). The reagents and conditions used in each assay are described in detail. The mean specific activity was 144 muCi/mug for 125I-labelled FgE and 82 muCi/mug for 125I-labelled FgD. Separation of antibody bound and free antigen was achieved using second antibody. The detection limits of the FgE, FgD and FgDneo assays were 0.8, 1.0 and 6.2 ng/ml respectively. The specificity of each assay with respect to fibrinogen and its degradation fragments has been assessed. Fibrinogen and fragment X cross-reacted markedly in both the FgE and FgD assays, whereas the cross-reaction of fibrinogen was abolished in the FgDneo assay, while the cross-reaction of fragment X was 10%, indicating gradual emergence of the neoantigenic site during digestion of fibriogen. The sensitivity, precision, and specificity of the radioimmunoassay systems described have major advantages over the existing procedures for the measurement of fibrinogen degradation products.

Antibody Specificity↗
PubMed1975

A detailed investigation of circulating IgE levels in a normal population.

Total circulating IgE levels were measured in a carefully selected normal population, using a highly sensitive double antibody assay. The mean level of 36.3 u/ml found in this group is much lower than that reported in all previous studies. No circadian rhythm was evident, but IgE levels varied slightly from day-to-day. IgE levels in 100 serum samples were compared using the double antibody assay and the Phadebas test kit, based on a solid phase technique. A poor correlation was obtained with values below 100 u/ml, however, there was an excellent correlation for samples with IgE levels above this figure.

Adolescent↗