Antidiuretic hormone (ADH) is a protein hormone created in the hypothalamus and stored in the posterior (back side) of the pituitary gland at the base of the brain.  ADH is responsible for conservation of water in the body.  This is done by decreasing the release of water from the kidneys into the urine.  In the kidneys, water is first filtered from the blood (along with waste products).  Much of this water is reabsorbed and delivered back to the blood.  ADH stimulates this reabsorption of water.  The end effect of high ADH levels is: 1) decreased urine, 2) increased water in the blood, and 3) increased blood pressure (due to a higher volume of water in the blood).

Where does it come from?

ADH is created in the hypothalamus (in the brain) an stored in the pituitary gland (at the base of the brain).

When and why is it secreted?

ADH is secreted in response to decreased water in the blood.  This decrease in water volume is detected by osmoreceptors in the hypothalamus.  These osmoreceptors do not directly measure blood pressure or water volume, but actually measure the amount of salt in the blood.  When the amount of water in the blood is too low, the blood becomes more "salty."  You can test this by putting a teaspoon of salt in a glass of water.  Taste the water before and after you leave the glass on a counter for a few days.  As the water evaporates, the water in the glass will become more salty.

What does ADH do?

1. ADH signals the kidneys to conserve water.  ADH tells the kidneys to decrease the amount of water released in urine.  
2. ADH also tells blood vessels to constrict (especially in the small arteries called arterioles).  This is called vasoconstriction.  ADH is sometimes called vasopressin.
3. ADH decreases sweating in order to conserve water.

What problems are caused by abnormal levels of ADH?

Syndrome of inappropriate ADH (SIADH) - a disease caused by an abnormally high level of ADH.  This causes: 1) high blood pressure, 2) water retention, and 3) low blood sodium levels.

Diabetes insipidus - a disease caused by inadequate secretion of ADH.  This can lead to massive amounts of fluids lost in the urine.  This symptoms include: 1) frequent thirst and drinking (polydipsia), 2) frequent urination (polyuria), 3) low blood sodium levels (hyponatremia), and 4) dehydration.

Alcohol consumption - alcohol inhibits the release of ADH.  This is why excess alcohol consumption can lead to frequent urination and dehydration.

How is ADH given as a medicine?

Because ADH is a protein, it can not be well absorbed in the gastrointestinal tract.  Therefore, ADH (called desmopressin) is given as a shot or a nasal spray.

What does ADH given as a medicine treat?

• Diabetes insipidus
• Bedwetting

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