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Biomedical subjects

J Landon

Publications and source records attributed to J Landon.

At least 145 records · Page 8Linked to original sources
PubMed1975

Stability of thyroxine and triiodothyronine in biological fluids.

The stability of thyroxine and triiodothyronine in serum has been investigated. Apparent levels of total thryroxine, as determined by two different protein-binding assays employing thyroxine-binding globulin as the binding protein, increased significantly in serum and plasma samples stored at room temperature and were signficantly lower in haemolysed samples. Values did not change significantly in samples stored at 4 degrees C, nor in samples stored at room temperature when determined by radioimmunoassay. Total triiodothyronine levels, as determined by radioimmunoassay, fell slightly on storage. Failure to appreciate the effect of storing samples at room temperature on apparent levels of total thyroxine, as determined by some protein-binding assays, could lead to an incorrect assessment of thyroid status.

Drug Stability↗
PubMed1975

Introduction.

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Journal Article↗
PubMed1975

Development and validation of a radioimmunoassay for peptides related to beta-melanocyte-stimulating hormone in human plasma: the lipotropins.

A radioimmunoassay is described for the measurement of human "beta-melanocyte-stimulating hormone" ("betah-MSH"). Two antisera have been used, one of which cross-reacts with synthetic betah-MSH as well as with the two larger pituitary peptides betah- and gammah-lipotropin (betah- and gammah-LPH) and the other mainly with betah-MSH and gammah-LPH. The sensitivity and reliability of the assay have been improved by employing a simple plasma extraction procedure, and the shelf-life of the iodinated betah-MSH tracer has been increased more than five-fold by storage in a concentrated human serum albumin solution. Using a 5 ml plasma sample the detection limit is 6 pg/ml. The mean resting "betah-MSH" level in normal subjects is 21 pg/ml (range 13-38 pg/ml) at 9 AM and 12 pg/ml (range 6-20 pg/ml) at 9 PM. Levels are considerably elevated (51-12,000 pg/ml) in patients with Addison's disease. Nelson's syndrome, Cushing's disease and the "ectopic" ACTH syndrome. After administration of insulin or pyrogen, the concentration of plasma "betah-MSH" increases in parallel with that of ACTH and they are approximately equivalent on a molar basis. The stability of purified betah- and gammah-LPH and endogenous "betah-MSH" when incubated in vitro in fresh blood or plasma are similar, in contrast to the less stable peptide synthetic betah-MSH. It is suggested that "betah-MSH" immunoreactivity in human plasma is due to betah- and gammah-LPH rather than betah-MSH.

Addison Disease↗
PubMed1974

A rapid, simple assay for digoxin.

An extremely rapid radioimmunoassay for digoxin is described which is precise over the range of concentrations required to determine whether, or not, a patient has digoxin toxicity. The assay is based on the use of (125)-iodine-labelled digoxin and of a gel equilibration technique for the separation of antibody-bound and free digoxin. The results obtained compare closely with those by a conventional radioimmunoassay and the technique is sufficiently simple to enable its performance by relatively inexperienced laboratory staff.

Binding Sites, Antibody↗
PubMed1973

Pituitary peptide.

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Adrenocorticotropic Hormone↗
PubMed1973

Comparison of corticotrophin and corticosteroid response to lysine vasopressin, insulin, and pyrogen in man.

Plasma corticotrophin (ACTH) and corticosteroid levels in response to lysine vasopressin (LVP), insulin hypoglycaemia, and pyrogen have been compared in seven subjects with normal pituitary adrenal function. Intramuscular vasopressin was a weak stimulus to corticotrophin release, peak values lying within the range 49 to 141 pg/ml. Insulin hypoglycaemia consistently caused a more noticeable increase, with peak levels between 114 and 364 pg/ml, while pyrogen was the most powerful, corticotrophin levels rising to between 209 and 1,725 pg/ml. Peak plasma corticosteroid levels showed less pronounced differences between the three tests, and correlated poorly with peak ACTH levels. Thus, relatively small acute changes in corticotrophin levels produce near-maximal adrenal stimulation. Under these conditions, plasma corticosteroid measurements do not accurately reflect circulating corticotrophin levels. These findings help to explain the physiological basis of several observations on the corticosteroid responses to these clinical test procedures.

11-Hydroxycorticosteroids↗