Increased Thymidine Kinase Activity in Human Thyroid Toxic Adenomas: Effects of Exposure to Epidermal Growth Factor In Vitro

The activity of thymidine kinase (TK-EC 2.7.1.21)-an enzyme functioning as a part of the pyrimidine salvage pathway of DNA synthesis-is closely related to growth processes. The aim of the study was to measure TK activity in homogenates of human thyroid tissue of the following types: non-toxic nodular goiter (NTNG)-macroscopically unchanged tissue, non-toxic adenoma (NTA), and toxic adenoma (TA) (obtained from patients, who-before the surgery-had been treated with thyrostatic drugs for thyrotoxicosis). Thyroid tissue was obtained from female patients subjected to subtotal thyroidectomy at the Department of Endocrine Surgery, Medical University of ód . Thyroid homogenates were incubated in the presence of epidermal growth factor (EGF), used in five different concentrations (0.1 ng ml, 1 ng ml, 10 ng ml, 100 ng ml, 1000 ng ml). TK activity was estimated by chromatographic measurements of the amount of the main reaction product-deoxythymidine monophosphate. Results: 1) We did not observe any significant difference between TK activity in the homogenates of the thyroid tissue collected from NTNG and NTA; TK activity was clearly higher in the homogenates of adenomatous tissue, collected from the patients with TA; 2) EGF increased TK activity in the homogenates of the macroscopically unchanged tissue, collected-during surgery-from the patients with NTNG, as well as in homogenates of thyroid tissue from NTA; 3) In case of hyperactive thyroid tissue, obtained from TA, EGF tended to increase TK activity, however, without any statistical differences. Our results confirm TK increased activity in hyperactive thyroid tissue. At the same time, the obtained data suggest a certain role of EGF in goiter formation in humans.