Kinetic Study of Immunoreactive Human Thyroglobulin

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Abstract
Thyroglobulin (Tg) can be detected in the circulation of normal subjects. Serum Tg is increased in patients with various thyroidal disorders including Graves' disease; however, little is known about Tg metabolism. Therefore, a kinetic study of human Tg was carried out in 13 normal men, 19–28 yr old, and 6 untreated hyperthyroid patients with Graves' disease, 3 men (22 to 25 yr old), and 3 women (21 to 63 yr old). Ten milligrams of Tg were injected as a bolus dose. Blood samples were collected before and 10min, and 2, 4, 6, 8,12 h and every 12 h up to 72 h after injection. Concentrations of serum Tg were measured by an RIA method developed in our laboratory. Anti- Tg antibody was not detected in any subject. Various indices of this kinetic study were calculated using single compartmental analysis. In 13 normal subjects, the mean serum concentrations of Tgwere 17 ± 12.6 (SD) ng/ml; mean half-life was 29.6 ± 2.8 h; distribution volumewas 11,210 ± 3,076 ml/60 kg body weight; fractional decay was 2.40 ± 0.22%/h;MCRwas 268.9 ± 87.8 ml/ h-60 kg; and release rate was 100.3 ± 50.2 μg/day-60kg.Serum concentrations of Tg were increased in four of the six untreated hyperthyroid patients with Graves' disease. Their Tg half-lives and MCR were within the normal range. In the two patients who had normal serum concentrations of Tg, the Tg half-lives were shorter and MCR were greater than in normal subjects. The release rates of Tg were increasedin all six of these patients. In summary, in hyperthyroid patients, Tg release is significantly greater than normal, whereas Tg metabolism is similar to that in normal subjects.

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