Final answer:
An injection of thyroxine to an otherwise normal rat will cause increased thyroid hormone synthesis and release.
Step-by-step explanation:
An injection of thyroxine to an otherwise normal rat will cause increased thyroid hormone synthesis and release.
Thyroxine is a hormone produced by the thyroid gland that plays a key role in regulating metabolism and growth. When thyroxine levels are low, the hypothalamus releases thyrotropin-releasing hormone (TRH), which stimulates the release of thyroid-stimulating hormone (TSH) from the anterior pituitary gland. TSH then binds to receptors on the thyroid gland, triggering the synthesis and release of more thyroid hormones (T3 and T4) into the bloodstream.
In this case, the injection of thyroxine would result in higher levels of the hormone in the rat's body, which would signal the hypothalamus and pituitary gland to decrease the production and release of TRH and TSH, respectively. This negative feedback mechanism helps maintain the balance of thyroid hormones in the body.