EFFECTS OF EPIDERMAL GROWTH-FACTOR (EGF) ON 3H-THYMIDINE INCORPORATION INTO DNA OF RAT-THYROID LOBES IN-VITRO, FOLLOWING DIRECT INTRATHYROIDAL IN-VIVO MICROINJECTIONS OF 6-HYDROXYDOPAMINE (6-OHDA) OR N-(2-CHLOROETHYL)-N-ETHYL-2-BROMOBENZYLAMINE (DSP-4)

The goal of our study was to examine the influence of local treatment of the thyroid lobes with sympathetic neurotoxins on the incorporation of 3H-thymidine into DNA of those lobes, incubated in vitro in the ex posure to epidermal growth factor (EGF) or without presence of that gr owth factor in the incubation medium. In order to obtain the thyroid d enervation, two catecholaminergic neurotoxins - 6-hydroxydopamine (6-O HDA) and N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4) - were a pplied in direct intrathyroidal microinjections. We observed that 6-OH DA significantly elevated 3H-thymidine incorporation, while DSP-4 reve aled only a tendency towards increasing the process in question. Also, the in vitro effects of EGF on the thyroid lobes, injected with 6-OHD A or DSP-4, were clearly different. Namely, EGF - in all the three exa mined concentrations - decreased the effect of 6-OHDA, whereas that gr owth factor - in concentrations of 10 ng/ml and 100 ng/ml - markedly i ncreased 3H-thymidine incorporation into DNA of DSP-4-injected thyroid lobes, when compared to controls or to DSP-4-injected group incubated without EGF (significant: effect vs. DSP-4 alone for EGF concentratio n of 100 ng/ml only). The differences in EGF effects on 3H-thymidine i ncorporation in vitro, depending on the neurotoxin used in vivo, are, up to now, not well understood.