Insulin-like growth factor I messenger ribonucleic acid expression in porcine thyroid follicles is regulated by thyrotropin and iodine

Hofbauer LC, Rafferzeder M, Janssen OE, Gartner R. Insulin-like growth factor I messenger ribonucleic acid expression in porcine thyroid follicles is regulated by thyrotropin and iodine. Eur J Endocrinol 1995;132:605–10. ISSN 0809–4643 Insulin-like growth factor I (IGF-I) has been shown to be released from thyrocytes in vitro. We investigated IGF-I mRNA expression during treatment with thyrotropin (TSH), forskolin and potassium iodide (KI) in intact porcine thyroid follicles ex vivo. Porcine thyroid follicles were prepared by collagenase digestion and cultured in the presence of TSH, forskolin or KI. After different incubation times, mRNA was isolated and examined by Northern hybridization with a porcine IGF-I cDNA probe of 405 bp in length. In untreated follicles no IGF-I mRNA was found, whereas in follicles stimulated with TSH an IGF-I mRNA of 7.0 kb was detected after 24 h, which persisted for another 24 h. Forskolin treatment mimicked the TSH effect, indicating that IGF-I mRNA expression may be stimulated by the adenylate cyclase pathway. Preincubation of the porcine follicles with KI decreased dose dependently the TSH-induced IGF-I mRNA expression, with complete inhibition at 10 μmol/l KI. These results suggest that TSH acts via the cAMP pathway to enhance IGF-I mRNA expression, which then may lead to an autocrine IGF-I stimulation. The IGF-I mRNA expression is under negative control of iodide. Roland Gärtner, Medizinische Klinik, Ludwig Maximilians University, Ziemssenstrasse 1, 80336 München, Germany