Direct effect of protirelin (TRH) on PB[123I] in autonomous thyroid adenoma.

In a retrospective study of 27 cases of iodine deficiency and/or latent primary hypothyroidism and in 16 cases of thyroid adenoma with hyperthyreosis the routine radioiodine uptake test was combined with a protirelin (TRH) test. After TRH infusion, [PB*I] and TSH increased significantly in all of these 27 patients who served as controls for the hyperthyroid patients. At the same time, the conversion rate Q rose in 14 of the control patients, but it dropped in 13 cases, thus indicating a TSH-induced discharge from the thyroid of radioiodine containing substances that were not bound to serum proteins. In nine of the 16 patients with autonomous adenoma, PB[*I] rose slightly, but Q did not increase significantly. In seven of the 16 adenoma patients, both PB[*I] and Q even dropped slightly in the absence of measurable serum TSH, thus indicating a negative direct effect of TRH on thyroid hormone metabolism.