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How do thyroid hormones reduce thyrotropin-releasing hormone and thyroid-stimulating hormone secretion?

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Hormone Many important physiological functions of vertebrates are controlled by steroid hormones.

Thyroid hormones regulate the secretion of thyrotropin-releasing hormone (TRH) and thyrotropin (thyroid-stimulating hormone) through a negative feedback control system within the hypothalamic-pituitary-thyroid axis.1

When circulating levels of thyroid hormones (thyroxine and triiodothyronine) are high, they act to inhibit the production and secretion of these regulatory hormones in two primary ways:

Direct Pituitary Action: Thyroid hormones travel to the anterior pituitary gland, where they bind to specific receptors on thyrotrophs. This action slows the release of thyrotropin and also inhibits the stimulatory effect that TRH has on these cells.234
Hypothalamic Action: Thyroid hormones exert an inhibitory influence on the hypothalamus, reducing the production of TRH.45

By suppressing both the hypothalamic signal (TRH) and the pituitary response (thyrotropin), the body effectively lowers the stimulation of the thyroid gland, allowing serum thyroid hormone concentrations to return to normal levels. Conversely, when thyroid hormone levels are low, this inhibition is lifted, leading to increased secretion of TRH and thyrotropin to restore balance.21