Paracrine interaction between thyrocytes and fibroblasts.
Cell free supernatants (conditioned medium) of isolated porcine thyroid follicles, stimulated with EGF (5 ng/ml) or TSH (1-1000 microU/ml), were tested for a mitogenic activity for fibroblasts. Whereas TSH-conditioned medium dose-dependently stimulated [3H]thymidine incorporation into DNA of fibroblasts, only a weak stimulation was found with EGF. However, when the changes in cell number were determined, a significant increase was only found with EGF-conditioned medium from thyroid follicles. The cause of this discrepancy is a dose-dependent stimulation of [3H]thymidine incorporation into fibroblasts by cAMP and thyroid hormones. Cyclic AMP, however, does not stimulate growth of fibroblasts. IGF I production is stimulated in fibroblasts by basal as well as EGF stimulated conditioned medium of thyroid follicles. In contrast, TSH-conditioned medium inhibited IGF I production in fibroblasts. Conditioned medium itself is free of detectable IGF I. As IGF I stimulates not only growth of fibroblasts, but also of thyrocytes, we conclude, that conditioned medium from thyrocytes stimulates IGF I production in fibroblasts, which itself stimulates fibroblast and thyrocyte growth.
D000818:Animals; D002455:Cell Division; D002478:Cells, Cultured; D004261:DNA Replication; D005347:Fibroblasts / Q000166:cytology; D006801:Humans; D012867:Skin / Q000166:cytology; D013552:Swine; D013961:Thyroid Gland / Q000166:cytology* / Q000187:drug effects; D013972:Thyrotropin / Q000494:pharmacology
D013972:Thyrotropin