Thyroid glands in patients with Graves' disease are sources of thyrotropin-binding inhibitory (TBI) activity.

In order to investigate the main sources of production of Graves' immunoglobulins, 4 women with Graves' hyperthyroidism, which relapsed after withdrawal of methimazole (MMI) therapy, were selected for this study. The patients underwent subtotal thyroidectomy after pre-operative treatment with MMI and Lugol's solution. Seven blood samples were obtained in each patient during surgery from: a peripheral vein, immediately before neck incision; the carotid artery; and the left and right inferior thyroid veins, respectively, before manipulation of the thyroid; and the left and right inferior thyroid veins, respectively, after surgical handling of the gland; a peripheral vein at the end of operation. Thyrotropin-binding inhibitory (TBI) activity was measured in all samples by a radioligand method. Serum TSH was also measured in those samples. There was a substantial increment of TBI in the thyroid veins compared with the activity in the carotid artery. The mean TBI was significantly higher after surgical handling of the thyroid lobes. The two lobes from each gland secreted differing levels of TBI, whereas the TSH concentrations were similar in all samples from each individual patients. We conclude that at least part of the TBI activity in patients with Graves' disease comes from the lymphocytic infiltration of the glands, and that differences in antibody production between the thyroid lobes may explain the difference in TBI activity in their respective thyroid veins.