Control of thyroid cell proliferation and goitrogenesis

Human thyroid cells proliferate during development and in adults in response to physiologic and pathologic stimuli. Under normal conditions, they turn over about once every 8 years. The main physiologic regulators are thyrotropin and iodide and, in disease, thyroid-stimulating and thyroid-blocking antibodies. Growth factors modulate proliferation in vitro, but their role in vivo is still unknown. Mitogenic effects are mediated via three major pathways: the cyclic AMP, protein tyrosine kinase, and the Ca(2+) phosphatidylinositol cascades. In this review, the role of these cascades in hyperthyroidism, congenital thyroid defects, and autonomous adenoma is analyzed.