Thymidine Kinase (EC 2.7.1.21) Activity in Homogenates of Human Thyroid Tissue, Following the Exposure to Epidermal Growth Factor (EGF) in vitro.
The activity of thymidine kinase (TK - EC 2.7.1.21) was measured in human thyroid tissue homogenates incubated in vitro. This enzyme functions as a part of the pyrimidine salvage pathway involved in DNA synthesis. The thyroid tissue was obtained from the thyroids of patients thyroidectomized at the Department of Endocrine Surgery, Medical University of lodz because of: 1. non-toxic nodular goiter (NTNG): tissue macroscopically unchanged, woman 46 yrs; 2. non-toxic adenoma (NTA), woman 37 yrs; 3. toxic adenoma (TA), woman 45 yrs. The tissue was incubated for 4 hours in RPMI 1640 medium (Gibco), containing Hepes buffer, 15 % FCS and the examined substance - 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). The TK activity was measured according to Cheng and Prusoff (1974) as modified by Greger and Draminski (1989). The reaction products were separated by ascending chromatography. It was found that: 1. TK activity in thyroid tissue from NTNG and NTA did not significantly differ from control incubations without EGF, while it was significantly higher in the thyroid tissue from TA; 2. in the range of concentrations from 1 ng/ml to 1000 ng/ml, EGF increased TK activity in the macroscopically unchanged tissue from NTNG; 3. the incubation of the tissue from NTA with EGF resulted in the increase of TK activity in a concentration-dependent manner; 4. EGF stimulated TK activity in the tissue from TA, but the difference was significant only after the lowest EGF concentration. The obtained results suggest a possible role of EGF in the pathogenesis of NTNG, as well as of NTA and TA in humans.
Department of Endocrine Surgery, Medical University of Lodz, Lodz, Poland.
J
Brzezinski
M
Karbownik
A
Gesing
A
Lewinski
M
Klencki
J
Greger