Effects of activin A on deoxyribonucleic acid synthesis, iodine metabolism, and cyclic adenosine monophosphate accumulation in porcine thyroid cells.

We have recently shown the presence of activin A in human thyroid cells. To determine whether activin A affects the growth and function of the thyroid, we investigated its effects on DNA synthesis, iodine metabolism, and cAMP accumulation in cultured porcine thyroid cells. Activin A increased DNA synthesis. This effect was abolished by addition of follistatin but additively enhanced by epidermal growth factor. In contrast, activin A significantly reduced uptake and release of iodide by the thyroid and also TSH-induced cAMP accumulation but did not inhibit the cAMP accumulation induced by forskolin. These data indicate that activin A stimulates thyroid growth irrespective of cAMP accumulation and inhibits thyroid function.