Vasopressin-arginine vasopressin (ADH, antidiuretic hormone)

A neurohypophysial hormone.

A small polypeptide synthesized in the hypothalamus and secreted from the posterior pituitary.

A peptide hormone that controls the reabsorption of molecules in the tubules of the kidneys by affecting the tissue’s permeability.

The day to day stimulus for the release of ADH is hyperosmolality, which is sensed to the shrinking of neuron bodies in the hypothalamus.

This stimulus is abruptly  closed off when the osmolality is normal or low.

The emergency stimulus for the release of ADH is hypovolemia, which is sensed in the arterial circulation and overrides osmolality control.

Release of ADH increases vascular tone and regulates aquaporins in the luminal membrane of the principal cells in the collecting ducts of the kidney.

vasopressin is secreted by hypothalamic neurons in response to hypertonicity and decreased effective arterial blood volume.

Vasopressin promotes water retention by activating the vasopressin receptor 2 in the nephron‘s collecting system, inserting water channels in the apical membrane and increasing water permeability.

Non-osmotic stimuli of vasopressin release include nausea, pain, acute stress of psychosis or exercise, postoperative state, and drugs such as narcotics and tricyclic antidepressants.

Aquaporins allow for the movement of water across the previously impermeable confines of collecting ducts, preventing the excretion of water and resulting in concentrated urine.

Hypovolemia is a potent stimulus for the release of ADH with the body limiting water excretion.

Overt hypervolemia, seen in edematous disorders (CHF, cirrhosis) also stimulates the release of ADH in response to the perceived low effective arterial circulation.

Vasopressin stimulates the release of ACTH, which indirectly increases responsiveness of alpha-1 receptor in blood vessel smooth muscle, increasing vessel tone and blood pressure.

Increases peripheral vascular resistance, which in turn increases arterial blood pressure.

Has a role in homeostasis, and the regulation of water, glucose, and sodium in the blood.

Derived from a preprohormone precursor that is synthesized in the hypothalamus and stored in the posterior pituitary.

Most of it is stored in the posterior pituitary and released into the bloodstream, while some of it however, some of it as released directly into the brain, where it plays an important role in social behavior and bonding.

Regulates retention of water.

When vasopressin is released, it signals the kidneys to absorb water.

Ingestion of excess water rarely causes hyponatremia, as normal kidney function can eliminate up to 20 to 30 L of free water daily.

Develops in the context of an underlying disruption of free water elimination, usually as a result of arginine vasopressin (AVP) release or renal failure.

AVP, also known as antidiuretic hormone, is a peptide hormone produced by the hypothalamus and transported via axons to the posterior pituitary, from which it is released.

AVP is primarily responsible for regulating osmotic homeostasis of body fluids.

AVP also plays a minor role in volume homeostasis, acting mostly through vasopressin type 1A and type 2 receptors.

AVP receptor activation causes a decrease in excretion of free water.

Most total body sodium is extracellular and thus is a primary determinant of plasma tonicity.

An increase in plasma tonicity stimulates the thirst center to increase fluid consumption and causes release of AVP.

Arginine vasopressin days regulation can be caused by both osmotic and nonosmotic mechanisms.

Released with dehydrated and causes the kidneys to conserve water, thus concentrating the urine, and reducing urine volume.

Implicated in most hyponatremic disorders.

Hyponatremia associated with increased morbidity and mortality.

Levels are usually detectable at a plasma sodium concentration above 135 mmol per liter, and levels increase linearly with increasing sodium levels.

Vasopressin hormone may be secreted in response to inadequate circulation, or inappropriately secreted, and sometimes ectopically secreted, with no osmotic or hemodynamic stimulus.

When secreted without an osmotic or hemodynamic abnormality it is termed inappropriate.

At high concentrations raises blood pressure by inducing moderate vasoconstriction.

Increases urine osmolality and decreases water excretion.

Increases permeability to water of the cells of distal tubule and collecting duct in the kidney and thus allows water reabsorption and excretion of concentrated urine.

Vasopressin increases peripheral vascular resistance and thus increases arterial blood pressure minimally in healthy individuals.

In hypovolemic shock such as that which occurs during hemorrhage, it act as a significant factor to increase blood pressure, therefore it is involved in blood pressure regulation.

Vasopressin in the brain associated with short-term and long-term memory, and delayed reflexes, and is released into the brain in a circadian rhythm by neurons of the supraoptic nucleus.

Involved in aggression between males, and temperature regulation.

Associated with pair bonding between sexual partners.

Secreted from posterior puitary in response to reductions in plasma volume, in response to increases in the plasma osmolality, and in response to cholecystokinin by the small intestine.

Secretion reduced with increased plasma volume with inhibition of release from pressure receptors in veins, carotid arteries and in the atria.

Osmoreceptors in the hypothalamus increase secretion of vasopressin with increased plasma oncotic pressure.

Neurons in the supraoptic nuclei and paraventricular nuclei of the hypothalamus make vasopressin, and are osmoreceptors as well.

Vasopressin is produced in the above nuclei and it travels down the axons through the infundibulum within neurosecretory granules that are found within Herring bodies, localized swellings of the axons and nerve terminals.

Herring bodies carry the vasopressin directly to the posterior pituitary gland, where it is stored until released into the blood.

Alcohol is an agonist, and prevents water reabsorption.

Angiotensin II may stimulate its secretion.

Main stimulus for secretion is increased osmolality of plasma.

Reduced volume of extracellular fluid increases the release of vasopressin.

Arginine vasopressin has 4 receptors, in different tissues and manifesting different actions.

Oxytocin is very similar to that of the vasopressin, differing at only two positions and the two genes are located on the same chromosome .

Because it is similar to oxytocin, high levels can cause uterine contractions while oxytocin has a slight antidiuretic function.

Decreased vasopressin release or decreased renal sensitivity can leadsto diabetes insipidus, a condition with hypernatremia, polyuria, and polydipsia.

High levels of vasopressin secretion can lead to the syndrome of inappropriate ADH secretion (SIADH) with resultant hyponatremia and occurs in brain diseases, small cell lung carcinoma, perioperative period from surgical stress and some commonly medications, such as analgesics and antiemetics.

Vasopressin receptor antagonists can treat hyponatremia.

Hyponatremia can be treated pharmaceutically through the use of vasopressin receptor antagonists.

Its long-acting synthetic analogue desmopressin is used in conditions featuring low vasopressin secretion, as well as for control of bleeding in some forms of von Willebrand disease and haemophilia A and in extreme cases of bedwetting by children.

Infusions has been used as a second line of management in septic shock patients not responding to high dose of inotropes.

Exerts its antidiuretic function by binding to the V2 vasopressin receptor on the membrane of epithelial cells of the collecting duct of the kidney.

Acts via V1 receptors on vascular contractile elements.

Released during cardiac arrest as an adjunct to epinephrine.

Powerful vasoconstrictor.

Plasma levels are markedly increased in some patients with CHF.

Increased concentrations in some patients with CHF can cause vasoconstriction.

Elevated levels in plasma not useful, because it rapidly degrades in the circulation.

With euvolemic and hypovolemic hyponatremia have vasopressin levels that range from 1-10 pg per milliliter, levels that are within the normal range but still are inappropriately high in a hypotonic state.

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