As a consequence of increased TSH s

As a consequence of increased TSH secretion the thyroid gland undergoes rapid
growth, the colloid in the follicular lumen declines, and this leads to follicular
hypertrophy. In the rat, this growth phase can last for up to 3 months, at which time the
gland becomes desensitized to further TSH stimulation and growth stops; how this
regulation is achieved is not known. It is recognized that TSH acts in concert with various
growth factors, such as insulin-like growth factor 1 (IGF1), to regulate normal cell
proliferation . Other stimulatory growth factors
may be involved, e.g. IGF2, epidermal growth factor (EGF), whereas inhibitory factors,
such as transforming growth factor β (TGFβ), have been shown to inhibit the stimulatory
effect of TSH