The interaction between TSH and EGF receptor binding in thyroid cells was first demonstrated by Westermark et al. (1985), using suspension cultures of thyroid follicles, pre-incubation with TSH caused a significant increase in the binding of EGF to thyroid cells. We have previously described a similar phenomena using porcine thyroid cell monolayer preparations (Atkinson & Kendall-Taylor 1986). This increase in binding is caused by an increase in the number of EGF receptors expressed with no significant change in the binding affinity of the receptor. This observation may prove of interest with regard to the controversial nature of the trophic role of TSH and the difficulty in demonstrating a TSH trophic effect in vitro (Risdall et al. 1984; Valente et al. 1983).
The mechanism by which the TSH effect on EGF-binding is achieved is unclear, other than the observation that it is cyclic AMP mediated and involves protein synthesis. Since thyroid