Vasopressin

 ( Neuropeptides ) 

Mammalian vasopressin, also called antidiuretic hormone ( ADH), arginine vasopressin ( AVP) or argipressin,

A third function is possible. Some AVP may be released directly into the brain from the hypothalamus, and may play an important role in social behavior, sexual motivation and , and maternal responses to stress.

Vasopressin induces differentiation of stem cells into cardiomyocytes and promotes heart muscle homeostasis.

It has a very short half-life, between 16 and 24 minutes.

AVP also may have a variety of neurological effects on the brain. It may influence pair-bonding in voles. The high-density distributions of vasopressin receptor AVPr1a in prairie vole ventral forebrain regions have been shown to facilitate and coordinate reward circuits during partner preference formation, critical for pair bond formation.

A very similar substance, lysine vasopressin ( LVP) or lypressin, has the same function in and its synthetic version was used in human AVP deficiency, although it has been largely replaced by desmopressin.

1. Increasing the water permeability of distal convoluted tubule (DCT) and cortical collecting tubules (CCT), as well as outer and inner medullary collecting duct (OMCD & IMCD) in the kidney, thus allowing water reabsorption and excretion of more concentrated urine, i.e., antidiuretic. This occurs through increased transcription and insertion of water channels (aquaporin) into the apical membrane of collecting tubule and collecting duct epithelial cells.
   (2016). 9781455743773, Elsevier. ISBN 9781455743773
   Aquaporins allow water to move down their osmotic gradient and out of the nephron, increasing the amount of water re-absorbed from the filtrate (forming urine) back into the bloodstream. This effect is mediated by V2 receptors. Vasopressin also increases the concentration of calcium in the collecting duct cells, by episodic release from intracellular stores. Vasopressin, acting through cAMP, also increases transcription of the aquaporin-2 gene, thus increasing the total number of aquaporin-2 molecules in collecting duct cells.
2. Increasing permeability of the inner medullary portion of the collecting duct to urea by regulating the cell surface expression of , which facilitates its reabsorption into the medullary interstitium as it travels down the concentration gradient created by removing water from the connecting tubule, cortical collecting duct, and outer medullary collecting duct.
3. Acute increase of sodium absorption across the ascending loop of Henle. This adds to the countercurrent multiplication which aids in proper water reabsorption later in the distal tubule and collecting duct.

The hormone vasopressin also stimulates the activity of NKCC2. Vasopressin stimulates sodium chloride reabsorption in the thick ascending limb of the nephron by activating signaling pathways. Vasopressin increases the traffic of NKCC2 to the membrane and phosphorylates some serine and threonine sites on the cytoplasmic N-terminal of the NKCC2 located in the membrane, increasing its activity. Increased NKCC2 activity aids in water reabsorption in the collecting duct through aquaporin 2 channels by creating a hypo-osmotic filtrate.

• Vasopressin is released into the brain in a circadian rhythm by neurons of the suprachiasmatic nucleus.
• Vasopressin released from posterior pituitary is associated with nausea.
• Recent evidence suggests that vasopressin may have analgesic effects. The analgesia effects of vasopressin were found to be dependent on both stress and sex.

Many factors influence the secretion of vasopressin:

• Ethanol (alcohol) reduces the calcium-dependent secretion of AVP by blocking voltage-gated calcium channels in neurohypophyseal nerve terminals in rats.
• Angiotensin II stimulates AVP secretion, in keeping with its general pressor and pro-volumic effects on the body.
• Atrial natriuretic peptide inhibits AVP secretion, in part by inhibiting Angiotensin II-induced stimulation of AVP secretion.
• Cortisol inhibits secretion of antidiuretic hormone.
  Collège des enseignants d'endocrinologie, diabète et maladie (2012). 9782294722332, Elsevier Masson. ISBN 9782294722332

The AVP that is measured in peripheral blood is almost all derived from secretion from the posterior pituitary gland (except in cases of AVP-secreting tumours). Vasopressin is produced by magnocellular neurosecretory neurons in the paraventricular nucleus of hypothalamus (PVN) and supraoptic nucleus (SON). It then travels down the axon through the Pituitary stalk within neurosecretory granules that are found within Herring bodies, localized swellings of the axons and nerve terminals. These carry the peptide directly to the posterior pituitary gland, where it is stored until released into the blood.

There are other sources of AVP, beyond the hypothalamic magnocellular neurons. For example, AVP is also synthesized by parvocellular neurosecretory neurons of the PVN, transported and released at the median eminence, from which it travels through the hypophyseal portal system to the anterior pituitary, where it stimulates corticotropic cells synergistically with CRH to produce ACTH (by itself it is a weak secretagogue).

The structure of oxytocin is very similar to that of the vasopressins: It is also a nonapeptide with a disulfide bridge and its amino acid sequence differs at only two positions. The two genes are located on the same chromosome separated by a relatively small distance of less than 15,000 bases in most species. The magnocellular neurons that secrete vasopressin are adjacent to magnocellular neurons that secrete oxytocin, and are similar in many respects. The similarity of the two peptides can cause some cross-reactions: oxytocin has a slight antidiuretic function, and high levels of AVP can cause uterine contractions.

Comparison of vasopressin and oxytocin neuropeptide families:

Vasopressin has off-label uses and is used in the treatment of vasodilatory shock, gastrointestinal bleeding, ventricular tachycardia and ventricular fibrillation.

Vasopressin agonists are used therapeutically in various conditions, and 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 in mild haemophilia A) and in extreme cases of bedwetting by children. Terlipressin and related analogues are used as in certain conditions. Use of vasopressin analogues for esophageal varices commenced in 1970.

Vasopressin infusions are also used as second line therapy for septic shock patients not responding to fluid resuscitation or infusions of (e.g., dopamine or norepinephrine) to increase the blood pressure while sparing the use of catecholamines. These argipressins have much shorter elimination half-life (around 20 minutes) comparing to synthetic non-arginine vasopresines with much longer elimination half-life of many hours. Further, argipressins act on V1a, V1b, and V2 receptors which consequently lead to higher eGFR and lower vascular resistance in the lungs. A number of injectable arginine vasopressins are currently in clinical use in the United States and in Europe.