Antidiuretic hormone (ADH), also known as vasopressin, is a hormone produced by the hypothalamus and released by the pituitary gland in response to changes in blood volume and blood pressure. Its primary function is to regulate the amount of water in the body by controlling the amount of urine produced by the kidneys.
ADH acts on the kidneys by increasing their reabsorption of water from the urine back into the bloodstream, which helps to maintain blood volume and prevent dehydration. When there is a decrease in blood volume or an increase in blood osmolality (concentration of solutes in the blood), ADH is released to stimulate water reabsorption.
ADH also has other physiological functions, including vasoconstriction (narrowing of blood vessels), which can increase blood pressure, and regulation of social behavior, including aggression and sexual behavior.
Abnormalities in ADH production or function can lead to medical conditions such as diabetes insipidus, where the kidneys are unable to respond to ADH, resulting in excessive urine production and dehydration, and syndrome of inappropriate antidiuretic hormone (SIADH), where the body produces too much ADH, leading to water retention and dilutional hyponatremia (low sodium levels in the blood).