Control of thyroid cell and follicle growth: recent advances and current controversies.

The regulation of cell proliferation within the thyroid follicle is a coordinated and finely balanced process involving integration of the action of pituitary thyrotropin with the effects of permissive and inhibitory growth factors of autocrine and paracrine origin. Our understanding of the cellular interactions and intracellular signalling processes involved in thyroid follicular growth control has been considerably assisted by in vitro cell culture techniques that enable thyroid follicular cells to be maintained and studied under conditions closely approximating those in vivo.