The vasopressine or antidiuretic hormone ( AVP , arginine-vasopressine or ADH , Antidiuretic hormone ) is a peptide Hormone synthesized by the cores supraoptic and paraventriculaire of the Hypothalamus and released by the posterior Hypophyse. It has mainly a antidiuretic action (reduction in the volume of the urines).
Structure
The vasopressine is a new polypeptide comprising amino-acid, whose two groupings Cystéine are connected by a Pont disulfide (Cys1 - Cys6). The sequence of the amino-acids is presented Ci-dessous.
H3N+─Cys─Tyr─Phe─Glu─Asp─Cys─Pro─Arg─Gly─NH2
Although the vasopressine and the Ocytocine have close structures (seven amino-acids jointly), these two hormones have very different effects.
Effects
The vasopressine has a antidiuretic action: it decreases the volume of the urines by increasing the permeability to water of the collecting tube (mainly by increasing the synthesis of Aquaporine 2, transmembrane pore on the apical/urinary side).
In pharmacology, the vasopressine is used for its effect vasoconstrictor (contraction of the vessels). That however requires important amounts of vasopressine, which explains why under the physiological conditions, the vasoconstriction due to the ADH is observed little.
Regulation
The circulating quantity of vasopressine is controlled by the Osmolarité and the blood pressure (more precisely, by the Volumétrie). On the level of the right auricle, Barorécepteur S analyze the blood Pressure. In the event of fall of pressure, information is transmitted to the central Nervous system and the hypothalamus which increases the production of vasopressine.
the increase in the osmolarity is analyzed by the Osmorécepteur S of the third ventricle cerebral and also results in a rise of the secretion of vasopressine.
Mode of action
The vasopressine binds on receiving S (AVPR1) of the muscles of the vessels, and induced, via a protein G, the activation of a Phospholipase C and the increase in the intracellular concentration in Calcium. The Ion S Ca2+ thus released support the interactions between the Protéine S of Actine and Myosine, which leads to the contraction of the vessels. After the contraction, calcic channels open in the membrane of the rough reticulum endoplasmic (SERCA) which decrease the intracellular calcium concentration and thus to allow another contraction to occur.
At the renal level, the vasopressine binds on receivers (AVPR2) cells of the collecting Tube, which contributes, via a protein G, with the increase in the rate of AMPc. AMPc active of the proteins Kinase S of the type has which phosphorylent Aquaporine S (AQP2). The aquaporines (hydrous channels), which is initially present in cytoplasmic blisters, migrate towards the apical membrane where they facilitate the drainage duct towards renal interstitium, through the cells of the collecting tube.
Antagonists of the vasopressine
Various molecules are under development like antagonists of the vasopressine, which would allow, inter alia, to have a treatment of certain forms of Hyponatrémie (low salt concentration in blood). Among them, one can quote the Tolvaptan, tested in the event of Cardiac failure or hyponatremy, the Conivaptan, these two products being nonpeptide inhibiters.
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