Effects of forskolin on the morphology and function of the rat thyroid cell strain, FRTL-5: comparison with the effects of thyrotrophin

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Abstract
The effect of diterpene forskolin, a potent stimulator of cyclic AMP (cAMP) in the rat thyroid cell strain FRTL-5, was compared with that of TSH. Forskolin stimulated both the release of cAMP into the culture medium and the accumulation of cAMP in the cytoplasm in a dose-dependent manner, within the range of 0·1–1000 μmol/l. Maximum cAMP concentrations were reached within 15 min of stimulation with forskolin. This is comparable with the effects of TSH. Forskolin also induced morphological changes in cultures of FRTL-5 cells, producing conspicuous cell retraction with arborization and numerous microvilli on the cell surface, specific reorganization of the microfilaments and modulation of the distribution of tubulin and fibronectin. Morphological changes induced by forskolin were always observed 20 to 30 min earlier, and in a higher percentage of cells, than the changes induced by TSH. Cell proliferation, however, was stimulated more effectively by TSH than by forskolin. These observations suggest that TSH might exert its effect on the morphology and growth of FRTL-5 cells, at least in part, through cAMP. The control of morphology and growth might not, however, be regulated solely by the adenylate cyclase and cAMP system. J. Endocr. (1986) 111, 397–405