ADH: Antidiuretic Hormone
Definition
Antidiuretic Hormone is a small protein secreted by part of the brain called the pituitary gland. Antidiuretic hormone is also known as ADH, or vasopressin. Antidiuretic hormone binds to receptors on cells in the kidney and blood vessels to affect the body. Many species use antidiuretic hormone. It increases the amount of water absorbed by the kidney and increases blood pressure. ADH has an antidiuretic action that prevents the production of dilute urine and so is antidiuretic.
A syndrome of inappropriate secretion of ADH results in the inability to put out dilute urine perturbs fluid and electrolyte balance, and causes nausea, vomiting, muscle cramps, confusion and convulsions. This syndrome may occur in association with oat-cell lung cancer, pancreatic cancer, prostate cancer, and Hodgkin’s disease as well as a number of other disorders.
ADH is produced in the hypothalamus and stored in the pituitary gland. It’s released from there into the bloodstream, and it affects how the kidneys work by letting them know how much water they need to keep in or get out of the body.
Deficiency of Antidiuretic Hormone (ADH)
A rare water metabolism disorder called central diabetes insipidus is sometimes the cause of ADH deficiency. Central diabetes insipidus is marked by a decrease in either the production of ADH by our hypothalamus or the release of ADH from our pituitary gland.
Common symptoms include excessive urination, which is called polyuria, followed by extreme thirst, which is called polydipsia.
Patients with central diabetes insipidus are often extremely tired because their sleep is frequently interrupted by the need to urinate. Their urine is clear, odorless, and has an abnormally low concentration of particles.
Central diabetes insipidus can lead to severe dehydration if it’s left untreated. Our body won’t have enough water to function.
This disorder is not related to the more common diabetes mellitus, which affects the level of the hormone insulin in our blood.
Function and Effects of Antidiuretic Hormone (ADH)
Antidiuretic Hormone or ADH regulates the body’s water retention. It is released from the brain when the body is dehydrated and causes the kidneys to conserve water, thus concentrating the urine and reducing urine volume. At high concentrations, it also raises blood pressure by inducing moderate vasoconstriction. In addition, it has a variety of neurological effects on the brain, having been found, for example, to influence pair-bonding in voles. The high-density distributions of vasopressin receptor AVPr1a in prairie vole ventral forebrain regions have been shown to facilitate and coordinate reward circuits during partner preference formation, critical for pair bond formation.
ADH has three main effects:
- Increasing the water permeability of distal convoluted tubule and collecting duct cells in the kidney, thus allowing water reabsorption and excretion of more concentrated urine, i.e., antidiuresis. This occurs through increased transcription and insertion of water channels into the apical membrane of distal convoluted tubule and collecting duct epithelial cells. Aquaporins allow water to move down their osmotic gradient and out of the nephron, increasing the amount of water re-absorbed from the filtrate (forming urine) back into the bloodstream. This effect is mediated by V2 receptors.
- Increasing permeability of the inner medullary portion of the collecting duct to urea by regulating the cell surface expression of urea transporters, which facilitates its reabsorption into the medullary interstitium as it travels down the concentration gradient created by removing water from the connecting tubule, cortical collecting duct, and outer medullary collecting duct.
- Acute increase of sodium absorption across the ascending loop of henle. This adds to the countercurrent multiplication which aids in proper water reabsorption later in the distal tubule and collecting duct.
Water Reabsorption and Antidiuretic Hormone (ADH)
The body uses antidiuretic hormone to retain water and increase blood pressure. As the main organ responsible for water retention in the body, the kidney is directly affected by antidiuretic hormone. The kidney is made of millions of units called nephrons. Nephrons filter blood through a series of tubules, which absorb water, salt and other things needed by the body. Below is a diagram of the kidney, including the structure of the nephron. Antidiuretic hormone binds to receptors on the surface of cells in the collecting duct of the nephrons.
Aquaporins are like doors in a nightclub; they let water in and out of the cell. When the doors open, people enter and leave, but because the nightclub is empty, more people go in, rather than out. Similarly, when there is more water inside the nephron than in the blood, when the gates open, water flows in the blood. This causes the body to hold more water and increases the volume of blood, which in turn, increases blood pressure.
