Effect of stimulation and suppression of the thyroid gland upon production of iodoprotein in man

Abstract

Iodinated components of serum were studied in 6 normal subjects and 10 patients with nontoxic goiter. After administration of I 125, serum specimens were analyzed by column chromatography using anion exchange resin (Dowex 1 × 2) and radioactivity was measured in 4 fractions: iodoprotein, iodotyrosine, iodothyronine and iodide. After 2 weeks, about 25 per cent of the radioactivity was found in the iodoprotein fraction of serum of normal subjects and 44 per cent in that of goitrous patients. Butanol-insoluble iodine (BII) was determined in 36 normal subjects and 26 patients with nontoxic goiter; the mean BII was 26 per cent of the total protein-bound iodine in the normal group, and 45 per cent in that of the goitrous group. The authors suggest that butanol-insoluble iodoprotein is present in serum of normal subjects but is in much larger amounts in that of goitrous patients. Production of iodoprotein could be suppressed by administration of thyroxin. Administration of thyroid-stimulating hormone (TSH) to normal subjects doubled production of iodoprotein and iodothyronine, but caused a more irregular response in patients with goiter. Gel filtration through Sephadex G-100 and salting-out in potassium phosphate showed that iodoprotein from goitrous subjects resembles iodoalbumin. Iodoprotein synthesis is a major pathway of iodine metabolism in patients with nontoxic goiter. This pathway is regulated by thyrotropin as it can be suppressed by thyroxin and activated by TSH.