Hypothalamus-Pituitary Axis and Hormones

The hypothalamus releases hormones that stimulate or inhibit the pituitary gland, which in turn releases hormones that affect target tissues. This creates a feedback loop where hormones regulate each other's release.

Growth hormone-releasing hormone (GHRH), thyrotropin-releasing hormone (TRH), corticotropin-releasing hormone (CRH), gonadotropin-releasing hormone (GnRH), and dopamine. These hormones stimulate or inhibit the release of anterior pituitary hormones.

Growth hormone (GH), thyroid stimulating hormone (TSH), adrenocorticotropic hormone (ACTH), luteinizing hormone (LH), follicle-stimulating hormone (FSH), and prolactin. These hormones act on specific target tissues to regulate growth, metabolism, and reproduction.

Anti-diuretic hormone (ADH) and oxytocin. These hormones are released in response to electrical signals from the hypothalamus.

Somatropin is a synthetic version of human growth hormone (GH) that acts directly on GH receptors to increase GH levels. Mecasermin is a synthetic version of IGF-1 that acts on IGF-1 receptors to stimulate growth.

Somatostatin and its analogs (octreotide and lanreotide) are used to treat acromegaly and gigantism by reducing the release of growth hormone. Pegvisomant blocks GH receptors, preventing GH from binding and signaling.

A hormone produced primarily by the liver in response to GH. It plays a role in growth, metabolism, and insulin sensitivity.

A hormone that inhibits the release of growth hormone. It binds to SST receptors on the pituitary gland.

Somatropin and mecasermin stimulate IGF-1, which inhibits insulin secretion and hepatic glucose production, potentially leading to hypoglycemia.

Mecasermin has a higher likelihood of causing hypoglycemia compared to somatropin because it enhances the hypoglycemic effects of other diabetic medications.

Mecasermin, due to its potential for adverse effects when administered intravenously.

Bromocriptine (slightly selective D2 receptor agonist) and Cabergoline (highly selective D2 receptor agonist) are used to suppress prolactin secretion from the pituitary gland.

Cabergoline has a longer half-life compared to Bromocriptine. Cabergoline is more likely to cause nausea, vomiting, and orthostatic hypotension.

Mecasermin, to prevent hypoglycemia.

Goserelin and Leuprolide are GnRH super-agonists, mimicking the action of endogenous GnRH but with prolonged stimulation, leading to a downregulation of LH and FSH. Degarelix is a GnRH antagonist, directly blocking GnRH receptors and inhibiting LH and FSH release.

Nafarelin is typically administered as a nasal spray, whereas goserelin is administered as a subcutaneous implant.

Drugs like Urofollitropin (Bravelle), follitropin alpha (Gonal-F), follitropin beta (Follistim), menotropins (Menopur, Repronex), choriogonadotropin alpha (Ovidrel), chorionic gonadotropin (Pregnyl, Profasi), GnRH super agonists like Gonadorelin (Factrel), Goserelin, histrelin, leuprolide, nafarelin, and triptorelin. These drugs are contraindicated in pregnancy because they increase FSH levels, leading to potential misdiagnosis of primary ovarian failure, and they can trigger a serious adverse event, ovarian hyperstimulation syndrome (OHSS).

Cabergoline (Dostinex) is a medication used to treat hyperprolactinemia. It works by specifically targeting D2 dopamine receptors, effectively reducing prolactin levels.

Bromocriptine (Parlodel) acts similarly to cabergoline, targeting D2 dopamine receptors to control hyperprolactinemia.

Cabergoline is an agonist that binds to dopamine D2 receptors. This interaction inhibits prolactin release from lactotropes. The drug's metabolism doesn't involve the CYP enzyme system; instead, it undergoes extensive hepatic hydrolysis with a lengthy half-life of about 65 hours. The main drug interactions associated with cabergoline involve alpha receptor agonists (e.g., clonidine), beta receptor agonists (e.g., albuterol), and antipsychotics (e.g., aripiprazole).

Desmopressin (DDAVP) selectively acts on V2 vasopressin receptors, leading to decreased water excretion in the kidneys. It also stimulates these receptors outside the kidneys, increasing Factor 8 and von Willebrand factors. In contrast, conivaptan (Vaprisol) works as an antagonist for both V1a and V2 vasopressin receptors. This action promotes increased water excretion in the kidneys via the collecting ducts.

Desmopressin and conivaptan act on the body's water balance in contrasting ways. Desmopressin is used to treat conditions like diabetes insipidus, nocturnal enuresis, and von Willebrand disease, while conivaptan is a valuable therapy for managing hyponatremia in patients with heart failure, cirrhosis, or syndrome of inappropriate antidiuretic hormone secretion (SIADH).

A protein found in the thyroid gland, responsible for transporting iodine into the cell.

The enzyme that oxidizes iodide and attaches it to tyrosine residues on thyroglobulin.

The process of attaching iodine to tyrosine residues, which are amino acids found in thyroglobulin.

The process of linking two iodotyrosine molecules together to form T3 and T4, the active thyroid hormones.

The process of the thyroid gland releasing thyroid hormones (T3 and T4) into the bloodstream.

A drug that inhibits both thyroid peroxidase (TPO) and 5' deiodination

A drug that inhibits thyroid peroxidase (TPO) but is more potent than PTU.

The most potent thyroid hormone - five times more potent than T4. It increases metabolism and influences growth and development.

Drugs that reduce the effectiveness of propylthiouracil (PTU) by interfering with its mechanism of action.

A synthetic hormone that acts as an agonist for the thyroid receptor, treating hypothyroidism. It is 100% T4, a precursor to T3, and stimulates the same receptors as naturally occurring T4.

A synthetic hormone that acts as an agonist for the thyroid receptor, treating hypothyroidism. It is 100% T3.

A synthetic hormone that acts as an agonist at nuclear T3 receptors, treating hypothyroidism. It is a combination of 20% T3 and 80% T4.

A drug that competitively inhibits iodine transport via the NIS (Na+/I- symporter). It is used to treat thyroid storm and for pre-operative preparation for thyroid surgery.

Beta-blockers are used in patients with thyroid disorders to manage symptoms such as palpitations, tachycardia, and anxiety. They are particularly helpful in patients with hyperthyroidism or thyroid storm.

Desmopressin is used to treat diabetes insipidus, a condition where the body produces too little ADH (antidiuretic hormone). This leads to excessive urination and dehydration. Desmopressin acts as an ADH analog, helping the kidneys retain water and reduce urination.

Conivaptan is a drug used to treat hyponatremia, a condition characterized by low sodium levels in the blood. It works by blocking the action of ADH, promoting water excretion and raising sodium levels.

Octreotide and lanreotide are synthetic analogs of somatostatin, a hormone that regulates growth hormone secretion. They act as agonists at somatostatin receptors, inhibiting the release of hormones like growth hormone, insulin, and glucagon.

Octreotide and lanreotide, somatostatin analogs, can cause side effects like bradycardia (slow heart rate), fluctuations in blood sugar levels (hypoglycemia or hyperglycemia), and impaired thyroid function (usually hypothyroidism).

FSH analogs can cause side effects like headache, depression, and edema (swelling) in both men and women. Gynecomastia (breast enlargement) is a specific side effect observed in males.

TSH, FSH, and LH are all hormones released from the anterior pituitary gland. However, TSH release is regulated by thyrotropin-releasing hormone (TRH), while FSH and LH release is stimulated by gonadotropin-releasing hormone (GnRH).

Diabetes insipidus, a condition marked by excessive urination and dehydration, is caused by insufficient production of ADH. Desmopressin, an ADH analog, is prescribed to help the body retain water and reduce excessive urination.

SIADH (Syndrome of Inappropriate Antidiuretic Hormone Secretion) causes the body to retain excessive water, leading to hyponatremia (low sodium levels). Conivaptan, an ADH antagonist, helps reduce water retention, thereby raising sodium levels.

The HPA axis is a complex system involving the hypothalamus, pituitary gland, and target tissues. The hypothalamus releases hormones that regulate the pituitary gland, which in turn secretes hormones that act on target tissues. This is a feedback loop where hormones regulate each other's release.

A hormone produced primarily by the liver in response to GH. It plays a role in growth, metabolism, and insulin sensitivity.

Mecasermin must be administered subcutaneously. Administering mecasermin intravenously can lead to adverse effects.

Reduces the effectiveness of propylthiouracil (PTU) by decreasing its ability to inhibit TPO.

The uptake of iodine (I-) by the thyroid gland is the first step in thyroid hormone synthesis. This process is facilitated by the sodium-iodide symporter (NIS), a protein found in the thyroid cell membrane.

Once inside the thyroid gland, iodide is oxidized to iodine. This process is catalyzed by the enzyme thyroidal peroxidase (TPO). Iodine then becomes attached to tyrosine residues on thyroglobulin, a protein found in the thyroid follicles.

Two iodotyrosine molecules are coupled together by an ether linkage to form iodothyronines, which include T3 (triiodothyronine) and T4 (thyroxine).

Propylthiouracil (PTU) is a medication used to treat hyperthyroidism by inhibiting the enzyme thyroidal peroxidase (TPO). It also blocks the conversion of T4 (thyroxine) to T3 (triiodothyronine).

Methimazole is another medication used to treat hyperthyroidism. It is more potent than PTU and specifically inhibits the enzyme thyroidal peroxidase (TPO).

Triiodothyronine (T3) is the most active form of thyroid hormone. It is five times more potent than thyroxine (T4).

Thyroid stimulating hormone (TSH) is produced by the pituitary gland and acts on the thyroid gland to stimulate the production and release of T3 and T4.

A drug used to treat hyperprolactinemia, which is a condition characterized by excessive prolactin production. Cabergoline has a high selectivity for dopamine D2 receptors, which are responsible for inhibiting prolactin release from the pituitary gland.

Bromocriptine is another drug that targets dopamine D2 receptors, leading to decreased prolactin release. It is also used clinically to treat hyperprolactinemia.

Cabergoline acts as an agonist at dopamine D2 receptors, which inhibits the release of prolactin. It's unique for its high selectivity and does not undergo CYP metabolism. It has a half-life of about 65 hours, suggesting long-term effects. It's important to consider potential drug interactions with alpha and beta receptor agonists as well as antipsychotics.

Desmopressin is a selective agonist at V2 vasopressin receptors, a crucial component of the body's water balance system. It increases water reabsorption in the kidneys and stimulates the production of key clotting factors. Conivaptan, on the other hand, acts as an antagonist for both V1a and V2 vasopressin receptors, leading to increased water excretion from the kidneys.

Desmopressin helps regulate water balance by increasing water reabsorption in the kidneys. It is clinically used to treat diabetes insipidus, nocturnal enuresis, and von Willebrand disease. Conivaptan, by increasing water excretion, is valuable in managing hyponatremia and is sometimes used for patients with heart failure, cirrhosis, or SIADH.

FSH analogs like Urofollitropin, follitropin alpha, follitropin beta, and menotropins are contraindicated in pregnancy. These drugs increase FSH levels, which can mimic the hormonal pattern of primary ovarian failure. They also pose a risk of triggering a serious adverse event, ovarian hyperstimulation syndrome (OHSS).

GnRH super agonists like Goserelin, Leuprolide, and Nafarelin are commonly used in hormonal therapies for conditions like prostate cancer and endometriosis. They act as powerful stimulators of GnRH receptors initially, leading to a surge in hormone production, but ultimately cause a downregulation of GnRH receptors, resulting in a decrease in LH and FSH production.

Cabergoline is a safe and effective treatment for hyperprolactinemia due to its high selectivity for D2 dopamine receptors, which inhibit prolactin release. It has a long half-life, allowing for once-weekly dosing. The most frequent side effects are nausea and vomiting, but it is generally well-tolerated by most patients.