Final answer:
High levels of thyroxine lead to decreased release of thyrotropin-releasing hormone (TRH) and subsequently lower production of thyroid-stimulating hormone (TSH), maintaining hormone balance through a negative feedback loop.
Step-by-step explanation:
When the levels of thyroxine, also known as tetraiodothyronine (T4), are high in the blood, this condition acts on a negative feedback loop involving the hypothalamus and the pituitary gland. As a consequence, the release of thyrotropin-releasing hormone (TRH) from the hypothalamus is inhibited or decreased. Consequently, the anterior pituitary gland's secretion of thyroid-stimulating hormone (TSH) is also reduced.
Due to this decrease in TSH, the stimulation of the thyroid gland is lessened, leading to a reduction in the secretion of thyroid hormones, including T3 (triiodothyronine) and T4. This elegant system of checks and balances is known as the hypothalamic-pituitary-thyroid axis. It ensures the levels of thyroid hormones in the bloodstream remain within a healthy range, thus maintaining the body's metabolic balance.