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Title: The development of immunological assays of parathyroid hormone and calcitonin for the assessment of mineral homeostasis in pregnancy and the neonate
Author: Abbott, Stephen R.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1979
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Development and characterisation of radioimmunoassays for parathyroid hormone (PTH) and calcitonin were undertaken. These assays were applied to the study of the maintenance of mineral homeostasis during pregnancy and in the neonatal period. The PTH assay developed represents one in which many of the problems encountered in applying the radioimmunoassay technique to the measurement of the circulating hormone have been overcome. Loss of immunochemical homogeneity on radioiodination of PTH was offset by the adoption of suitable procedures for purifying the labelled hormone, and the useful lifetime of 125I-BPTH in the assay system was extended by the inclusion of a simple pre-assay gel-filtration step. The analytical significance of various non-specific interferences in the assay system has been minimised. In particular non-specific adsorption of PTH has been reduced to a consistently low level. The behaviour of plasma samples in the assay system was also rigorously studied and the assay procedure finally accepted for routine use as a result of these investigations has proved a reliable analytical method for the study of circulating immunoreactive PTH. The radioimmunoassay for calcitonin was also optimised with regard to each of its components. Assay peformance was significantly improved by modifying the radioiodination procedure used to produce 125i-human calcitonin; sodium metabisulphite was shown to produce chemical damage to the calcitonin molecule and consequently was replaced by cysteamine-hydrochloride. Immunisation procedures undertaken in the rabbit resulted in the production of anti-calcitonin sera, but these compared unfavourably with an available goat anti-calcitonin serum in the radioimmunoassay system. The assay developed using the goat antiserum was capable of detecting as little as 20 ng/l human calcitonin in plasma. Specific calcitonin receptors have been demonstrated in preparations derived from rabbit kidney tissue and a radioreceptor assay for calcitonin established. Calcitonin-receptor interaction was investigated and the relationship between the hormone's immunochemical and biological behaviour is discussed. Membrane preparations isolated from human renal tissue, by the procedure used to prepare calcitonin receptors from rabbit kidney, failed to display calcitonin binding activity. The radioimmunoassays developed were used to study plasma mineral homeostasis in a series of 227 pregnancies from a Clinical Trial in which the effect of maternal vitamin-D supplementation (1000 International Units/day) was investigated. Analytical data obtained showed that there was little tendency for pregnant women to become significantly hyperparathyroid, relative to non-pregnant controls, even though PTH concentrations increased significantly from the end of the first trimester to term. There was no evidence to support the hypothesis that calcitonin is of particular physiological importance to the mother in pregnancy. Infant plasma calcitonin was raised relative to maternal concentrations throughout the first week of life, whilst plasma PTH concentrations were relatively low at delivery but increased as post-natal maturation occurred. Although maternal vitamin-D status was shown to be a significant factor influencing extracellular calcium concentration in the newborn period, it appeared to be less important with regard to both maternal and neonatal plasma PM and calcitonin concentration. The relationship between PTH and calcitonin and vitamin-D in pregnancy and the newborn period is discussed with particular reference to the pathogenesis of late onset neonatal hypocalcaemia.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available