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Thyrotrophin (4-256 µU/ml) promoted an increase in the rate of release of radioiodine from the organic iodine pool of cultured porcine thyroid cells in follicular formations. This action of TSH was antagonized by low concentrations of epidermal growth factor (EGF; 0·1–5 nmol/l). The maximal effect of EGF was reached by 0·5 nmol/l. EGF (0·5–5 nmol/l) also inhibited the stimulatory effect of 8-chloro cyclic AMP (0·06–1·0 nmol/l) on radioiodine turnover. Exposure of thyroid cultures to media with a calcium concentration of 17·7 µmol/l (1% of normal) resulted in a very marked increase in the rate of release of radioiodine. The effect of TSH in low-calcium media was to inhibit the increased release of radioiodine, and EGF (0·5 nmol/l) antagonized this inhibitory effect of TSH. The calcium ionophore, A23187 [GenBank] , stimulated radioiodine release in a dose-dependent fashion, and EGF (1·7 nmol/l) inhibited this response. Fluid transport in thyroid monolayers was stimulated by prostaglandin E₂ (PGE₂; 1 µmol/l). EGF (5 nmol/l) also stimulated fluid transport, but antagonized the effect of PGE₂ added subsequently. It was concluded that EGF exerted acute antagonistic effects on thyroid cell responses in vitro to cyclic AMP and agents promoting accumulation of cyclic AMP in time-frames too short for these inhibitory effects to be attributable to the dedifferentiative effect of the growth factor.

Journal of Endocrinology (1991) 128, 213–218