A relatively small (peptide) molecule that isAntidiuretic hormone (ADH): A relatively small (peptide) molecule that isreleased by the pituitary gland at the base of the brain after being madenearby (in the hypothalamus). ADH has an antidiuretic action that preventsthe production of dilute urine (and so is antidiuretic). A syndrome ofinappropriate secretion of ADH results in the inability to put outdilute urine, perturbs fluid (and electrolyte) balance, and causes nausea,vomiting, muscle cramps, confusion and convulsions. This syndrome may occur in associationwith oat-cell lung cancer, pancreatic cancer, prostate cancer, and Hodgkin'sdisease as well as a number of other disorders. ADH also can stimulatecontraction of arteries and capillaries. ADH is also known as vasopressin.