Is it ensure, insure, or assure?
vasopressin va·so·pres·sin (vā'zō-prěs'ĭn)
Abbr. VP A hormone, related to oxytocin, that is secreted by the posterior lobe of the pituitary gland, constricts blood vessels, raises blood pressure, stimulates intestinal motility, and reduces the excretion of urine. Also called antidiuretic hormone.
See antidiuretic hormone.