Alternative names for anti-diuretic hormone

Vasopressin; arginine vasopressin; AVP; ADH

What is anti-diuretic hormone?

Anti-diuretic hormone is a hormone made by special nerve cells found in an area at the base of the brain known as the hypothalamus. The nerve cells transport anti-diuretic hormone down their nerve fibres (axons) to the posterior pituitary gland where the hormone is released into the bloodstream. Its most important role is to conserve the fluid volume in the body by reducing the amount of water passed out in the urine. It does this by allowing water in the urine to be reabsorbed back into the body in a specific area of the kidney. This action causes more water return to the bloodstream, increasing the concentration of the urine and reducing the amount of water loss. Anti-diuretic hormone also helps to control blood pressure by acting on the kidneys and the blood vessels. Higher concentrations of anti-diuretic hormone cause blood vessels to constrict (become narrower) and this increases blood pressure. 

How is anti-diuretic hormone controlled?

The release of anti-diuretic hormone from the pituitary gland into the bloodstream is controlled by a number of factors. A decrease in blood volume or low blood pressure, which occurs during dehydration or when large volume of blood loss occurs (also known as haemorrhage), is detected by sensors (baroreceptors) in the heart and large blood vessels. These stimulate anti-diuretic hormone release.

Secretion of anti-diuretic hormone also occurs if the concentration of salts in the bloodstream increases, for example as a result of not drinking enough water on a hot day. This is detected by special nerve cells in the hypothalamus (osmoreceptors) which stimulate anti-diuretic hormone release. The release of anti-diuretic hormone is also stimulated by thirst, nausea, vomiting and pain, and acts to keep up the volume of fluid in the bloodstream at times of stress or injury. Alcohol prevents anti-diuretic hormone release, which causes an increase in urine production and dehydration.

What happens if I have too much anti-diuretic hormone?

High levels of anti-diuretic hormone cause the kidneys to retain water in the body. Syndrome of Inappropriate Anti-Diuretic Hormone secretion (SIADH) is a condition where excess anti-diuretic hormone is released when it is not needed. In this condition, excessive water retention dilutes the blood, giving a characteristically low salt concentration, a condition known as hyponatraemia. Excessive levels of anti-diuretic hormone might also be caused by side-effects of drugs and diseases of the lungs, chest wall, hypothalamus or pituitary. Some tumours (particularly lung cancer), can produce anti-diuretic hormone.

What happens if I have too little anti-diuretic hormone or if my kidneys are insensitive to anti-diuretic hormone?

When there is insufficient production anti-diuretic hormone, or when the kidneys are unable to respond to it, the body is unable to conserve water effectively. This leads to excessive water loss through urine, (known as Vasopressin-Related Polyuria), resulting in increased urine volume, dehydration, and a drop in blood pressure.

AVP Deficiency Syndrome (previously called Central Diabetes Insipidus) occurs when too little anti-diuretic hormone is produced, usually due to damage to the hypothalamus or pituitary gland. This may result from a tumour, trauma, surgery, inflammation or infection. In this condition, the kidneys do not receive enough ADH, leading to excessive urination and thirst.

AVP Resistance Syndrome (previously called Nephrogenic Diabetes Insipidus) arises when the kidneys are insensitive to anti-diuretic hormone, despite adequate or even high hormone levels. This resistance may be due to medications – most notably lithium – chronic kidney damage, or rare genetic defects that impair the function of anti-diuretic hormone receptors in the kidneys.

Both AVP deficiency and AVP resistance syndromes are characterised by excessive thirst and the production of large volumes of pale, diluted urine, which can quickly lead to dehydration if untreated.

Treatment:

• AVP Deficiency Syndrome is managed with desmopressin (DDAVP) which is a synthetic form of the anti-diuretic hormone, along with adequate hydration. 
• AVP Resistance Syndrome is treated by maintaining hydration, discontinuing the causative medication (if applicable), and by using medications such as thiazide diuretics and anti-inflammatory agents like ibuprofen to reduce urine output.

In contrast, Primary Polydipsia – a condition involving compulsive or excessive water intake – leads to appropriately low anti-diuretic hormone levels. This reflects the body’s effort to excrete excess water and maintain normal blood concentration.