Information AboutVasopressin |
| CATEGORIES ABOUT VASOPRESSIN | |
| neuropeptides | |
| posterior pituitary hormones | |
| neuroendocrinology | |
| renal physiology | |
Arginine vasopressin ('''AVP'''), also known as '''argipressin''' or '''antidiuretic hormone''' ('''ADH'''), is a human Hormone that is mainly released when the body is low on Water ; it causes the Kidney s to conserve water by concentrating the Urine and reducing urine volume. It has also various functions in the Brain and Blood Vessel s. A very similar substance, lysine vasopressin ('''LVP''') or '''lypressin''', has the same function in Pig s and is often used in human therapy. These vasopressins are Peptide Hormone s produced in the Hypothalamus . Most of it is stored in the Posterior Part of the Pituitary Gland to be released into the blood stream; some of it is also released directly into the brain. PHYSIOLOGY Control Vasopressin is secreted from the posterior pituitary gland in response to reductions in Plasma volume and in response to increases in the plasma Osmotic Pressure . Secretion in response to reduced plasma volume is activated by Pressure Receptors in the Vein s, Atria , and Arteriole s. Secretion in response to increases in plasma osmotic pressure is mediated by Osmoreceptor s in the Hypothalamus . The neurons that make vasopressin, in the Supraoptic Nucleus and Paraventricular Nucleus , are themselves osmoreceptors, but they also receive synaptic input from other osmoreceptors located in regions adjacent to the anterior wall of the third ventricle. These regions include the Organum Vasculosum Of The Lamina Terminalis and the Subfornical Organ . Many factors influence the secretion of vasopressin; for instance, Ethanol and Caffeine reduce vasopressin secretion. The resulting decrease in water reabsorption by the kidneys leads to a higher Urine output. Angiotensin II also stimulates the secretion of vasopressin. The vasopressin that is measured in peripheral blood is almost all derived from secretion from the posterior pituitary gland (except in cases of vasopressin-secreting tumours). However there are two other sources of vasopressin with important local effects:
Peripheral actions Vasopressin acts on three different Receptor s, termed V1a , V1b and V2 . The receptors are differently expressed in different tissues, and exert different actions:
Actions within the brain Vasopressin released within the brain has many actions:
In recent years there has been particular interest in the role of vasopressin in social behavior. It is thought that vasopressin, released into the brain during sexual activity, initiates and sustains patterns of activity that support the pair-bond between the sexual partners; in particular, vasopressin seems to induce the male to become aggressive towards other males. Evidence for this comes from experimental studies, in several species, which indicate that the precise distribution of vasopressin and vasopressin receptors in the brain is associated with species-typical patterns of social behavior. In particular, there are consistent differences between monogamous species and promiscuous species in the distribution of vasopressin receptors, and sometimes in the distribution of vasopressin-containing axons, even when closely-related species are compared. Moreover, studies involving either injecting vasopressin agonists into the brain, or blocking the actions of vasopressin, support the hypothesis that vasopressin is involved in aggression towards other males. There is also evidence that differences in the vasopressin receptor gene between individual members of a species might be predictive of differences in social behavior. STRUCTURE AND RELATION TO OXYTOCIN The vasopressins are Peptide s consisting of nine Amino Acid s (nonapeptides). The amino acid sequence of arginine vasopressin is Cys - Tyr - Phe - Gln - Asn - Cys - Pro - Arg - Gly , with the cysteine residues form a Sulfur Bridge . Lysine vasopressin has a Lysine in place of the arginine. The structure of that make vasopressin are adjacent to magnocellular neurons that make 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 vasopressin can cause uterine contractions. Here is a table showing the superfamily of vasopressin and oxytocin neuropeptides: ROLE IN DISEASE Decreased vasopressin release or decreased renal sensitivity to vasopressin leads to Diabetes Insipidus , a condition featuring Hypernatremia (increased blood Sodium content), Polyuria (excess urine production), and Polydipsia (thirst). High levels of vasopressin secretion ( Syndrome Of Inappropriate Antidiuretic Hormone , SIADH) and resultant Hyponatremia (low blood sodium levels) occurs in Brain diseases and conditions of the Lung s. In the Perioperative period, the effects of surgical stress and some commonly used medications (e.g. Opiates , Syntocinon , Anti-emetic s) lead to a similar state of excess vasopressin secretion. This may cause mild hyponatraemia for several days. PHARMACOLOGY 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 extreme cases of bedwetting by children. Terlipressin and related analogues are used as Vasocontrictor s in certain conditions. Demeclocycline , a tetracycline antibiotic, is sometimes used to block the action of vasopressin at the kidney in hyponatremia due to inappropriately high secretion of vasopressin (SIADH, see above), when fluid restriction has failed. A New class of medication ( Conivaptan , Tolvaptan , Relcovaptan , Lixivaptan ) acts by inhibiting the action of vasopressin on its Receptor s (V1 and V2), with tolvaptan acting on V1a and V2 and the remainder mainly on V1a receptors. Vasopressin infusion has been used as a second line of management in Septic Shock patients not responding to high dose of inotropes (e.g., Dopamine or Epinephrine ). REFERENCES |
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