Studies on the in vitro trophic effects of a novel thyromimetic

Since fibroplasia has been reported in rats treated with SK&F l-94901, a novel thyromimetic drug, studies were undertaken to investigate: (i) the trophic effect of the agent in a number of in vitro proliferation assays and (ii) its ability to cause in vitro cell transformation. There was no effect in any of these assays when SK&F l-94901 was incubated directly with the cells, so consideration was given to the possibility that the chemical could be having an indirect mitogenic effect by stimulating the production of growth factors from other tissues such as the pituitary. However, since the conditioned medium from pituitary superfusates also failed to show any evidence of a mitogenic effect, the proliferative lesions do not appear to be associated with an over-production of growth factors by the pituitary. The in vivo growth-promoting activity of SK&F l-94901 does not appear to be caused by a direct mitogenic effect in the cells resulting in cell transformation or by stimulation of growth factors from the pituitary.