Vasopressin (arginine vasopressin, AVP; antidiuretic hormone, ADH) is a peptide hormone formed in the hypothalamus, then transported via axons to the posterior pituitary, which releases it into the blood. Vasopressin is also known as antidiuretic hormone. Its main function is to increase the permeability of epithelial cells and reabsorb water to produce antidiuretic effects. It can also cause the contraction of the gastrointestinal and gall bladder. Vasopressin increases the reabsorption of water by increasing the permeability of renal collecting duct epithelial cells, producing antidiuretic effects, and can also shrink peripheral blood vessels and cause the intestine, gallbladder and bladder to contract. The antidiuretic activity unit of vasopressin is determined by an anesthetized animal boost test.
AVP has two principle sites of action: the kidney and blood vessels.
The primary function of AVP in the body is to regulate extracellular fluid volume by regulating renal handling of water, although it is also a vasoconstrictor and pressor agent (hence, the name “vasopressin”). AVP acts on renal collecting ducts via V2 receptors to increase water permeability (cAMP-dependent mechanism), which leads to decreased urine formation (hence, the antidiuretic action of “antidiuretic hormone”). This increases blood volume, cardiac output and arterial pressure.
A secondary function of AVP is vasoconstriction. AVP binds to V1 receptors on vascular smooth muscle to cause vasoconstriction through the IP3 signal transduction pathway and Rho-kinase pathway, which increases arterial pressure; however, the normal physiological concentrations of AVP are below its vasoactive range. Studies have shown, nevertheless, that in severe hypovolemic shock, when AVP release is very high, AVP does contribute to the compensatory increase in systemic vascular resistance.
The chemical nature
It is white powder, slightly odor, pH 3.4–4.0 in aqueous solution, and isoelectric point of 10.9. This product is extracted from the posterior pituitary gland of cows, pigs and other animals. This product has both anti-diuretic and hypertensive effects. The anti-diuretic effect is rapid, but the maintenance time is only 2–8h. However, it is not good for the heart when raising blood pressure. Generally, it is not clinically used as a blood pressure drug.
The mechanism of action
After vasopressin binds to the V2 receptor on the peritubular membrane of epithelial cells in the distal convoluted tubules and collecting ducts, it activates the adenosylase in the membrane and increases the production of cAMP in epithelial cells; the production of cAMP is increased by activating protein kinase in epithelial cells, the activation of protein kinase makes the vesicles containing water channels located near the lumen membrane inlay on the lumen membrane, increasing the water channels on the lumen membrane, thereby increasing the water permeability. When vasopressin is lacking, the water channels on the luminal membrane can be concentrated in the depression of the cell membrane, and the latter form swallowing vesicles into the cytoplasm, which is called internalization. Therefore, the water channel on the lumen membrane disappears and is impermeable to water. The vesicles of these water-containing channels are embedded in the lumen membrane or enter the cell from the lumen membrane, which can adjust the permeability of the lumen membrane to water. The basal side membrane is free to pass water. Therefore, water passes through the luminal membrane and enters the cell freely through the basal side membrane to enter the capillaries and be reabsorbed.
The application
- For the treatment of central diabetes insipidus.
- Used for initial treatment of polyuria after brain surgery or head trauma.
- It is also used for abdominal muscle relaxation where other drugs are not effective.
- It is also used in the adjuvant treatment of acute hemorrhage caused by gastrointestinal diseases such as esophagus and gastrointestinal tract.