Vasopressin

Vasopressin, also known as antidiuretic hormone (ADH) and arginine vasopressin (AVP), is a hormone secreted by most mammals, including humans. It functions primarily to help the body regulate and retain water and constrict blood vessels. It plays a role in helping the body stay hydrated and in blood pressure control. Early twenty-first-century research also indicates that vasopressin may affect the brain and could play a role in autism and in how animals bond.

A synthetic version of vasopressin is available and marketed in injectable and nasal spray forms. These are administered for a variety of medical conditions, including diabetic insipidus, some bleeding disorders, severe bedwetting in children, and septic shock.

Production and Function

The hormonal form of vasopressin is a polypeptide (a chain of amino acids) produced by the hypothalamus. It moves from the hypothalamus to the pituitary gland to be released as needed.

Vasopressin is an antidiuretic, which means it prevents the body from losing water through urination. Its production is triggered by neurons called osmoreceptors, located in the hypothalamus. The osmoreceptors detect the amount of solutes such as plasma and other organic components present in the blood. When the osmoreceptors determine that solutes are becoming concentrated—when the body is losing fluid due to profuse sweating, for instance—they signal the hypothalamus to release vasopressin and prevent the loss of more fluids through urination. The hormone is sent to the kidneys where it helps to create small channels that send solute-free water back into the bloodstream to dilute the solutes in the blood while reducing the amount of urine and increasing its concentration.

Retaining fluids in this way can be important because the osmoreceptors that cause thirst are not as sensitive as those that prevent urination. Humans, which are about 60 percent water by mass, can reach a state of dehydration before becoming thirsty, and vasopressin helps in conserving necessary fluids to maintain a relatively stable water content level.

Although its most significant function is in preventing excessive water loss through urination, vasopressin actually is named for its effects on the body's vascular system. While its effect on the human circulatory system is relatively minor, high levels of vasopressin can have a significant effect on blood pressure in other mammals. Decreases in blood pressure or blood volume can stimulate the release of vasopressin, which can constrict blood vessels. Incidents of hemorrhage that result in the loss of 15 to 20 percent of blood volume can trigger the release of vasopressin in mammals, including humans.

Sometimes the ability of the body to produce vasopressin is affected by damage to the pituitary gland or hypothalamus resulting from a head injury, an infection, a tumor, surgery, loss of blood flow to the gland, or a genetic problem. Impaired vasopressin production can lead to a condition called central diabetes insipidus. Characterized by extreme thirst that generates excessive urine output—as high as 16 liters or approximately 4.25 gallons in a single day—central diabetes insipidus is not common and is not often life threatening, assuming adequate amounts of water are available for consumption. It is treated through the administration of synthetic vasopressin.

Pharmaceutical Uses

In addition to treating central diabetes insipidus, the synthetic form of vasopressin can be used for a number of other conditions. It is approved to prevent and treat abdominal distention following surgery. It also is used during abdominal roentgenography—an ultrasound procedure used in the diagnosis of problems of the liver, spleen, gallbladder, and other abdominal organs—to reduce interference from gas shadows. Because it restricts the amount of urine produced, it has sometimes been used to treat extreme instances of juvenile bedwetting.

Continuing Research

In the early twenty-first century, researchers began making some connections between vasopressin and social behavior. Studies on the connection between two similar hormones, vasopressin and oxytocin, have indicated that some brain receptors react to both hormones. Oxytocin is generally associated with the generation of good feelings and happiness while vasopressin appears to be linked to aggression and anxiety. Animal studies have indicated that males are more susceptible to responding with aggression when high levels of vasopressin are present. Some studies have indicated that vasopressin is linked to how mammals process sensory input such as sounds and smells.

These connections led researchers to look at a possible role for vasopressin in autism, a condition that causes behavioral issues for about one in every sixty-eight American children. In one study, researchers from Stanford University were not able to determine whether the presence of a certain level of vasopressin causes autism, but they did conclude that its presence at certain levels could predict how children with autism would perform on a test that measured their perception of the perspectives of other people. Autistic children with low levels of vasopressin did not score well on this test; non-autistic children with low vasopressin levels showed no difference in scoring.

Another study, conducted by researchers at the University of Queensland in Australia, looked at behavior patterns and vasopressin levels of almost 7,400 twins from Finland and their siblings. The researchers examined the relationships of these twins and their partners, all of whom had been in relationships with a partner for at least a year. Their work indicated a connection between a variation in the gene for a vasopressin receptor and infidelity. The study received great attention and was touted as an indicator that cheating in a relationship has a genetic cause, but the researchers themselves urged caution in interpreting the results and suggested that much more study was required.

Bibliography

"Diabetes Insipidus." MedlinePlus. U.S. National Library of Medicine. Web. 27 Jan. 2016. https://www.nlm.nih.gov/medlineplus/diabetesinsipidus.html

Landau, Elizabeth. "Vasopressin Emerges as Hormone of Interest in Autism Research." Scientific American. Scientific American, a division of Nature America, Inc., 11 Sept. 2015. Web. 27 Jan. 2016. http://www.scientificamerican.com/article/vasopressin-emerges-as-hormone-of-interest-in-autism-research/

"Media Heralds the Discovery of 'Infidelity Gene.'" National Health Services. National Health Services, United Kingdom, 16 Feb. 2015. Web. 27 Jan. 2016. http://www.nhs.uk/news/2015/02February/Pages/Media-heralds-the-discovery-of-the-infidelity-gene.aspx

"Test ID: AVP—Arginine Vasopressin, Plasma." Mayo Clinic. Mayo Foundation for Medical Education and Research. Web. 27 Jan. 2016. http://www.mayomedicallaboratories.com/test-catalog/Overview/80344

"Vasopressin (Injection Route)." Mayo Clinic. Mayo Foundation for Medical Education and Research. Web. 27 Jan. 2016. http://www.mayoclinic.org/drugs-supplements/vasopressin-injection-route/description/DRG-20066681

"Vasopressin Replacement." Cedars-Sinai. Cedars-Sinai. Web. 27 Jan. 2016. https://www.cedars-sinai.edu/Patients/Programs-and-Services/Pituitary-Center/Conditions-Treatments-and-Diagnostics/Drug-Therapy/Vasopressin-Replacement.aspx

Zietsch, Brendan P., Lars Westberg, Pekka Santtila, and Patrick Jern. "Genetic Analysis of Human Extrapair Mating, Heritability, Between-Sex Correlation, and Receptor Genes for Vasopressin and Oxytocin." Evolution and Human Behavior 36.2 (March 2015): 130–136. Web. 27 Jan. 2016. http://www.ehbonline.org/article/S1090-5138%2814%2900131-7/abstract