Quantitative studies of iodine metabolism

This thesis describes a series of investigations of the quantitative aspects of iodine metabolism in relation to thyroid disease. Few studies in this field have combined accurate chemical measurement of the quantities of iodine involved at each stage with radioiodine measurements of the dynamic aspects of iodine metabolism. The work described here is primarily concerned with the development of reliable microchemical techniques for the determination of iodine in body fluids and tissues. The application of these techniques and of radioiodine measurements to the study of iodine metabolism in healthy subjects and in patients with thyroid disease is described. A simplified chemical method for the microdetermination of iodine in biological samples was developed which proved accurate and reliable in routine laboratory use. An alternative method of iodine microdetermination by neutron activation analysis was also investigated but consistent results were not obtained. The successful chemical procedure involved chloric acid digestion of organic material followed by colerimetric determination of iodine utilising the iodide catalysed ceric sulphate - arsenions acid redox reaction. In the application of this technique particular emphasis was placed on the determination of the protein-bound fraction of blood iodine (P.D.I.), which is the most direct index at present available of the level of circulating thyroid hormone. The relationship between serum P.D.I. and thyroid function was investigated in a large series of subjects with normal and disordered iodine metabolism. The dietary iodine supply in the West of Scotland was studied by chemical determination of the iodine content of food and water. Fish was shown to be by far the richest source of dietary iodine available. The figures obtained for milk and eggs were high in comparison with earlier published values. The low iodine content of Glasgow tap water indicated that the dietary supply from this source was of little significance. Diet histories of hospital patients revealed that subjects with simple goitre had a significantly smaller iodine intake than normal individuals. A method for urinary iodine analysis was developed and its accuracy assessed. The urinary excretion of iodine was measured in a series of patients with thyroid disease and in a normal control group. Faecal excretion of iodine was similarly studied in a small number of subjects. The level of the plasma inorganic iodine, which is of great importance in the regulation of thyroid function, was determined by a specific activity technique and the validity of the procedure was demonstrated