Antidiuretic hormone, vasopressin.

Also known as Arginine vasopressin; Antidiuretic hormone; AVP; Vasopressin. ADH is also a test (water restriction test) that measures the amount of antidiuretic hormone (ADH) in the blood. ADH is found in the body and it is also given as a medication.
ADH is a hormone stored in the posterior pituitary gland in the brain, regulating water levels in the body. ADH interacts with the kidneys to increase total body water increasing blood volume and blood pressure. The release of ADH is controlled by cells called osmoreceptors and baroreceptors. Osmoreceptors are specialized areas in a part of the brain called the hypothalamus. These cells measure the concentration of particles in the blood. When the concentration is high, the pituitary releases more ADH, causing more water to be retained to dilute the body fluids. When the concentration is low, the pituitary releases less ADH.
The heart also senses blood volume and blood pressure, and signals the pituitary to release more ADH when blood volume or blood pressure are low and less ADH when they are high.