A hormone synthesized in the hypothalamus and then transported to the blood to regulate extracellular fluid volume in the blood vessels and kidneys. It also plays a role in vasoconstriction. Vasopressin and oxytocin evolved from a single primordial neurohypophyseal hormone called vasotocin, which is present in lower vertebrates. Vasopressin, oxytocin, and their receptors are involved in regulating mating systems in several mammals.
Vasopressin (antidiuretic hormone)