Thymidine kinase activity in homogenates of rat thyroid lobes from euthyroid, hypothyroid and/or hyperthyroid rats incubated with EGF: studies ex vivo in vitro.
OBJECTIVE
To examine thymidine kinase (TK - ATP: thymidine 5'-phosphotransferase, EC 2.7.1.21) activity in homogenates of rat thyroid lobes incubated in vitro with epidermal growth factor (EGF).


METHODS
The thyroid lobes were collected from euthyroid, hypothyroid and/or hyperthyroid animals. Hypothyroidism was developed in the experimental rats by an administration of 0.1 % solution of propylthiouracil (PTU) in drinking water for 2 weeks, while hyperthyroidism was obtained by daily i.p. injections of L-thyroxine (50 microg/kg, B.W.), also for 2 weeks. After collecting, the thyroids were incubated for 4 hours in RPMI 1640 medium with an addition of 20 mM of Hepes buffer, 15% FCS, penicillin (200 U/ml), streptomycin (10 ug/ml) and with EGF (Sigma) (0.1 ng/ml, 10 ng/ml, 1000 ng/ml). The control lobes were incubated without any addition of EGF to the medium. TK activity was expressed as the amount of reaction products, measured by ascending chromatography.


RESULTS
1. in the absence of EGF, TK activity in the homogenates of thyroid lobes from hypothyroid rats was lower, while it was higher in the lobes from hyperthyroid animals, when compared to these obtained from euthyroid controls; 2. EGF in the concentration of 0.1 ng/ml or 1000 ng/ml decreased, while that in the concentration of 10 ng/ml increased TK activity in lobes collected from euthyroid or hyperthyroid rats; 3. in the tissue collected from hypothyroid rats, the addition of EGF (0.1 ng/ml or 10 ng/ml) caused a slight increase in TK activity versus hypothyroid controls - a tendency towards diminishing TK activity could be observed as parallel to increasing EGF concentration.


CONCLUSIONS
TK activity in the homogenates of rat thyroid lobes depends on the functional thyroid status and on applied EGF concentration in vitro.
Karbownik
M
M
Department of Thyroidology, Institute of Endocrinology, Medical University of Lodz, 91-425 Lodz, Poland.
Modrzejewska
H
H
Gesing
A
A
Greger
J
J
Lewinski
A
A
D000704:Analysis of Variance; D000818:Animals; D004353:Drug Evaluation, Preclinical; D004815:Epidermal Growth Factor / Q000627:therapeutic use*; D006980:Hyperthyroidism / Q000188:drug therapy*; D007037:Hypothyroidism / Q000139:chemically induced / Q000188:drug therapy*; D066298:In Vitro Techniques; D008297:Male; D051381:Rats; D017208:Rats, Wistar; D013937:Thymidine Kinase / Q000378:metabolism*; D013961:Thyroid Gland / Q000187:drug effects* / Q000201:enzymology
D004815:Epidermal Growth Factor; D013937:Thymidine Kinase