Protein composition of the thyroid colloid in patients with hyperthyroidism

Analysis of the protein composition of the thyroid colloid was performed in 28 patients operated on for hyperthyroidism. Fifteen of the patients were treated before the operation with carbimazole combined with thyroxine and 13 were treated with propranolol alone. Colloid was collected by micropuncture of single follicles in peroperative thyroid biopsies. The protein composition was analysed by microgel electrophoresis and densitometry, both in the colloid samples and in the supernatant fraction of homogenates of microbiopsies from the thyroid specimens. The analyses showed that, during treatment with carbimazole and thyroxine, the relative amount of the larger thyroglobulin aggregates (S-TG) was decreased compared with the relative amount observed in the colloid from normal thyroid tissue. In the hyperfunctioning thyroid tissue from the propranolol-treated patients the protein composition of the colloid was similar to that observed in normal tissue and the relative amount of the S-TG fractions was significantly higher than in the carbimazole- and thryoxine-treated group. It may be concluded that the increased release of thyroid hormones in hyperthyroidism is not combined with changes in the protein composition of the thryoid colloid. The decreased relative amount of the S-TG fractions in the thyroid colloid from patients treated with carbomazole and thryoxine was probably due to an insufficient capacity to iodinate thyroglobulin.