Vasopressin

ANTI DIURETIC HORMONE

Other name: Vasopressin; Arginine Vasopressin; AVP

ADH is a hormone secreted by the posterior lobe of the pituitary gland that constricts blood vessels, which is responsible in the rise of blood pressure , and reduces excretion of urine.

I will illustrate a simple diagram of ADH action in our body.

Posterior lobe --> anti diuretic (vasopressin) --> site of action for kidney --> reabsorption of water and fluid balance --> site of action for arterioles --> blood pressure

Anti diuretic hormone is a substance that decreases urine production. It causes the kidney to return more water to the blood, thus decreases the urine volume. Urine Output increases more than ten folds in the absence of ADH while in the presence of ADH, the kidneys retain water. ADH is produced by the hypothalamus and secreted by the posterior pituitary gland. Plasma osmolarity or concentration of solutes in blood, is the most important variable that regulates the anti diuretic hormone secretion. The plasma osmolarity is being sensed in the hypothalamus by neurons known as the osmoreceptors.

Two principle sites of action of AVP: kidney and bloodvessels.

Functions of AVP:
1. Regulates extracellular fluid volume
2. AVP is vasoconstriction.

Common disease related to ADH is Diabetes Insipidus. This condition may arise from either of two situations:
- Hypothalamic (central) diabetes insipidus- deficiency is the secretion of ADH from the posterior pituitary
- Nephrogenic diabetes insipidus- occurs when kidney is unable to respond to ADH

Major signs of either of the type of Diabetes Insipidus is: excessive urine production.

Test: ADH test
The test is performed if a disorder that affects the ADH level is suspected.
In some diseases, the normal release of ADH is altered, and the serum level of ADH must be tested to determine the cause. ADH may be measured as part of a "water restriction test" to more thoroughly investigate the cause of a disease.

Normal Values for ADH test:
Values of 0 to 4.7 pg/mL are normal.

Abnormally high may indicate:
-Acute porphyria (very rare)
-CNS infection
-CNS Tumor
-Post-surgery fluid imbalance
-SIADH (syndrome of inappropriate ADH)

Abnormally low may indicate:
-Damage to the pituitary gland
-Diabetes Insipidus (central or nephrogenic)
-Primary polydipsia


Reference:
http://www.cvphysiology.com/Blood%20Pressure/BP016.htm
http://www.vivo.colostate.edu/hbooks/pathphys/endocrine/hypopit/adh.html
http://healthguide.howstuffworks.com/adh-dictionary.htm
http://www.ecosci.jp/pdb/vasopressin.gif
http://www.umm.edu/ency/article/003702.htm
Principles of Anatomy & Physiology, Gerard J. Tortora, Bryan Derrickson