A nonapeptide neurohypophysial hormone related to oxytocin and vasotocin; synthetically prepared or obtained from the posterior lobe of the pituitary of healthy domestic animals. In pharmacologic doses vasopressin causes water retention and contraction of smooth muscle, notably that of all blood vessels; large doses may produce cerebral or coronary arterial spasm. SYN: antidiuretic hormone, Pitressin. [vaso- + L. premo, pp. pressum, to press down, + -in]
