Endocrine Pharmacology: Thyroid Hormones

Thyroid hormone receptors (TRs) bind to DNA (specifically to thyroid response elements, TRE, via their DNA-binding domain, TR-DBD) before binding to a ligand.

Free T3 and T4 are transported into the cell and then translocate to the nucleus.

Ligand binding to TR happens through the ligand-binding domain (TR-LBD). T3 has a higher binding affinity to TR than T4.

When T3/T4 binds to the TR bound to DNA, the co-repressor is 'kicked off'.

There are multiple receptor subtypes for T3 and T4. These subtypes differ in their tissue distribution and functional roles.

A set of interconnected endocrine glands that regulate the production and release of hormones via a chain reaction.

The control pathway involving the hypothalamus, pituitary gland, and thyroid gland. This axis regulates thyroid hormone production and secretion.

The hypothalamus releases thyroid-releasing hormone (TRH) which stimulates the pituitary to release thyroid-stimulating hormone (TSH). TSH then stimulates the thyroid gland to produce and release thyroid hormones (T3 and T4).

The process of creating and releasing thyroid hormones, T3 (triiodothyronine) and T4 (thyroxine), from the thyroid gland.

Synthetic versions of thyroid hormones used to treat hypothyroidism. They mimic the actions of naturally produced hormones.

Drugs that block the production of thyroid hormones. Used to treat hyperthyroidism.

A group of drugs used in the treatment of hyperthyroidism that interfere with the production of thyroid hormones. Examples include propylthiouracil (PTU) and methimazole (Tapazole).

Drugs that treat hyperthyroidism by slowing down the heart rate and reducing blood pressure. Examples include propranolol, atenolol, and esmolol.

A mechanism that regulates the production and release of thyroid hormones. It involves a feedback loop between the hypothalamus, pituitary gland, and thyroid gland.

A hormone produced by the hypothalamus that stimulates the release of thyroid-stimulating hormone (TSH) from the pituitary gland.

A hormone released by the anterior pituitary gland that stimulates the thyroid gland to produce and release thyroid hormones (T3 and T4).

The primary thyroid hormone responsible for increasing the body's metabolic rate.

A more potent thyroid hormone that is actively converted from T4 within cells.

The process by which thyroid hormones regulate their own production through a feedback loop.

The condition of having low thyroid hormone levels, leading to a decrease in metabolic rate.

The condition of having high thyroid hormone levels, leading to an increase in metabolic rate.

A synthetic hormone that mimics the action of TSH, used to stimulate thyroid function in diagnostic tests.

The mechanism by which thyroid hormones bind to specific receptors within cells, influencing gene expression and ultimately affecting various metabolic processes.

The process of converting inactive thyroid hormone (T4) to the active form (T3) in peripheral tissues.

A protein that binds to thyroid hormones in the bloodstream, transporting them to tissues.

A synthetic thyroid hormone medication containing 100% T4.

A synthetic thyroid hormone medication containing 100% T3.

A combination thyroid hormone medication containing both T4 and T3.

A condition that affects the thyroid gland caused by immune system attacks.

A drug that inhibits the production of thyroid hormones.

A drug that inhibits the production of thyroid hormones.

A drug that inhibits the production of thyroid hormones.

A synthetic medication containing T3 and T4.

A protein responsible for transporting thyroid hormones into cells.

A medication that decreases the effectiveness of thyroid hormone medications by increasing its metabolism.

A medication that decreases the effectiveness of thyroid hormone medication by inhibiting its peripheral activation.

A class of drugs that act by inhibiting the uptake of iodide into the thyroid gland. They share similar structural features and ionic size with iodide, allowing them to compete for the same binding sites on the Sodium-Iodide Symporter (NIS). This competitive inhibition disrupts iodide transport, leading to a decrease in thyroid hormone synthesis.

A potent medication used in the treatment of hyperthyroidism, often as a last resort. It works by directly destroying thyroid tissue using beta and gamma radiation, causing cell apoptosis and reducing thyroid hormone production.

A form of hyperthyroidism caused by an overproduction of thyroid-stimulating antibodies (TSI). These antibodies bind to the TSH receptor (TSH-R), leading to excessive thyroid hormone production.

A type of medication used to treat hyperthyroidism by interfering with the synthesis of thyroid hormones. These drugs block the activity of thyroid peroxidase, an enzyme crucial for the production of thyroid hormones, thereby reducing their production.

A medication used in the treatment of hyperthyroidism, it acts by blocking multiple biosynthetic steps involved in thyroid hormone production through negative feedback mechanisms. It inhibits both the synthesis and release of thyroid hormones, reducing the overall level of thyroid hormone in the body.

An over-the-counter medication used to treat hyperthyroidism by blocking iodine uptake into the thyroid gland. It competes with iodide ions for binding sites on the Sodium-Iodide Symporter (NIS), effectively reducing the uptake of iodide by the thyroid gland. This leads to a decrease in thyroid hormone synthesis due to the reduced availability of the essential building block, iodide.

One of the most common side effects of radioactive iodine treatment for hyperthyroidism. It occurs as a consequence of the radiation-induced destruction of thyroid tissue, reducing the ability of the gland to produce thyroid hormone.

Levothyroxine is preferred because it has a longer half-life, leading to more consistent and stable thyroid hormone levels. It also mirrors the natural production of T4 by the thyroid gland.

Levothyroxine's mechanism is to directly replace the deficient thyroid hormone (T4) in hypothyroidism. It restores the normal levels of thyroid hormones in the body.

Levothyroxine is used to treat hypothyroidism, a condition where the thyroid gland does not produce enough thyroid hormones. It is also used to replace thyroid hormones after surgery for thyroid cancer. In the past, it was also used to treat goiters, but this use is less common now.

Levothyroxine therapy is monitored by measuring the serum thyroid-stimulating hormone (TSH) levels. This is done to check if the treatment is effective and to adjust the dose if needed.

Elderly patients are more sensitive to thyroid hormones and may be at higher risk for side effects. Therefore, levothyroxine is typically started at a smaller dose in this population and is adjusted slowly to achieve the desired therapeutic effect.

Elevated TSH levels indicate that the thyroid gland is not producing enough thyroid hormones. In hypothyroidism, the pituitary gland releases more TSH in an attempt to stimulate the thyroid gland, resulting in elevated TSH.

Factors like age, cardiac function, and presence of other medications can affect the thyroxine dose. Elderly patients and those with heart disease may need lower doses. Interaction with other medications, especially those affecting metabolism, should be considered.

The goal of levothyroxine replacement therapy is to restore the serum TSH concentration to the normal range and relieve the symptoms of hypothyroidism. This means achieving a euthyroid state, where the body has normal thyroid hormone levels.