Vasopressin

Vincent du Vigneaud synthesized the vasopressin for the first time. It is also known as ADH(Antidiuretic hormone), Arginine Vasopressin(AVP), or argipressin. Vasopressin is a hormone that is produced by the neurons present in the hypothalamus location, it is first synthesized as peptide prohormone, and then it is converted into AVP. The converted AVP is then transported to the axon region of the neurons. From the axon, it is terminated in the posterior pituitary, and in response to the circulation of extracellular fluid hypertonicity. It induces the differentiation of the stem cells to form cardiomyocytes, this promotes the homeostasis of the heart muscle. It is said that the life span of vasopressin is half-life as it can live in between 16 to 35 minutes. 

The decrease in the arteriole volume of blood stimulates the secretion of the vasopressin. The ADH that is measured in the peripheral blood is derived from the secretion of vasopressin from the region of the posterior pituitary gland. Cortisol can inhibit the release of ADH. Let us see how it functions, what are its uses, side effects, and much more about this substance.

Arginine Vasopressin

Vasopressin can regulate the tonicity of the fluids situated in the body. These are released in the posterior pituitary region in response to the hypertonicity, this makes the kidneys reabsorb the solute-free water and then the tonicity is returned from the nephron via tubules to circulation. Now the tonicity of the body fluids is back to normal. A consequence of this reabsorption is concentrated urine and the reduced volume of urine. It has several neurological effects on the brain. A substance that is similar to vasopressin is lysine vasopressin(LVP); it is also known as lypressin which is found in pigs that perform the same function. The synthetic version of LVP is used in humans in case of deficiency. 

The ADH Action in Kidneys and CNS are:

• Kidney: 

There are three main effects:

1. It increases the permeability of water in PCT and CCT that is distal and cortical collecting tubes, also in the inner and outer medullary collecting ducts in the kidney. This helps in the reabsorption of water and the concentrated urine is excreted. This occurs due to the insertion of water channels in the apical membrane that is found in the collecting tubules and in the collecting duct epithelial cells, due to increased transcription. The aquaporins or the water channels allow the movement of water out of the nephron down the osmotic gradient. Thus the water is reabsorbed from the filtrate back to the bloodstream. This effect is done with the help of V2 receptors. ADH Vasopressin has the capability to increase the amount of calcium in the cells of the collecting duct. It can also increase the transcription of the aquaporin-2 gene through the action of cAMP, this in return increases the amount of aquaporin-2 gene molecules in the collecting duct.

2. By regulating the cell surface expression of the urea transporters, it increases the inner medullary portion of the collecting duct permeability to urea. It facilitates reabsorption in the medullary interstitium. It travels through the concentration gradient that is created for removing the water from certain ducts such as connecting tubules, outer medullary collecting duct, and cortical collecting duct. 

3. Across the ascending loop of the Henle, the acute increase in sodium absorption takes place. This can add the countercurrent multiplication which helps in the proper reabsorption of water in the collecting duct and the distal tubule. 

• Central Nervous System: 

The vasopressin that is released within the brain has many functions, a few of which are:

1. The neurons of the suprachiasmatic nucleus release the vasopressin in a circadian rhythm in the brain.

2. Nausea is associated with the release of the vasopressin in the posterior pituitary region. 

3. According to recent studies, it is suggested that vasopressin has analgesic effects. These effects are dependent on the sex of an individual and stress. 

Vasopressin Mechanism of Action

The ADH mechanism of action has two sites of action, one is kidneys and the other is blood vessels. 

Primarily AVP has Two Functions: 

1. During the process of circulation, in the kidney tubules of the nephron, the solute-free water is reabsorbed, where the AVP helps to increase the amount of reabsorption of the water.

2. The AVP can constrict the arterioles this can increase the peripheral vascular resistance and raises the blood pressure of the arterioles.

3. There is a possibility of another function, this AVP can directly be released from the hypothalamus to the brain. This can affect social behaviour, maternal responses to stress, and pair bonding.

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Vasopressin Use

• Vasopressin is used in the treatment of diabetes insipidus, which is caused due to the absence of naturally occurring pituitary hormone in the body. 

• In the conditions that occur after surgery or during the abdominal x-rays, vasopressin is used in the treatment of these situations.

• In adults who are in shock in such persons, vasopressin is used to raise the levels of blood pressure in an emergency setting. 

Vasopressin Side Effects

If a person is allergic to chlorobutanol or vasopressin, then he should not be treated with this drug. One has to mention to the caretaker or doctor that previously they had any coronary artery disease or heart problems, kidney disease, migraine headaches, asthma, or epilepsy. If the vasopressin is given to pregnant women in their second or third trimester then it can cause premature labour contractions. A breastfeeding woman has to avoid feeding the baby if she has taken the vasopressin for about two hours. It can also cause temporary side effects such as nausea, blanching of the skin, or stomach pain.

Common Side Effects Include:

• Tingling or feeling of numbness in the feet or hands.

• Loss of colour around the mouth or lips.

• Unusual changes found in the skin especially in the lower legs or feet.

• Trouble in breathing, chest pain, or tightness in the chest region.

• Weak pulse or slow heart rate.

• No urination.

• Low sodium level.

In order to avoid these side effects, the proper dosage has to be given, it is injected into the muscle or infused into the vein. To treat the diabetes insipidus, sometimes the doctor suggests taking the vasopressin in the form of a medicine dropper or nasal spray. 

Conclusion

Vasopressin is used to manage the deficiency of the antidiuretic hormone. It is the important regulator of the excretion of renal water. Vasopressin is a hormone that is produced by the neurons present in the hypothalamus location, it is first synthesized as peptide prohormone, and then it is converted into AVP. Vasopressin can regulate the tonicity of the fluids situated in the body. The ADH action has two sites of action, one is kidneys and the other is blood vessels.