Vasopressin Arginine (AVP-[Arg8]) is a peptide hormone. It is derived from a preprohormone precursor that is synthesized in the hypothalamus, from which it is liberated during transport to the posterior pituitary. Most of it is stored in the posterior part of the pituitary gland to be released into the blood stream; some of it is also released directly into the brain.  Arginene Vasopressin is a human hormone that is released when the body is low on water; it causes the kidneys to conserve water, but not salt, by concentrating the urine and reducing urine volume. It also raises blood pressure by inducing moderate vasoconstriction. It has various effects in the brain.

The vasopressins are peptides consisting of nine amino acids (nonapeptides). (NB: the value in the table above of 164 amino acids is that obtained before the hormone is activated by cleavage). The amino acid sequence of arginine vasopressin is Cys-Tyr-Phe-Gln-Asn-Cys-Pro-Arg-Gly, with the cysteine residues forming a sulfur bridge. Lysine vasopressin has a lysine in place of the arginine.

Vasopressin, as the name tells, increases the resistance of the peripheral vessles and thus increases arterial blood pressure. This effect is almost inexistant in healthy individuals, however it becomes an important compensatory mechanism for restoring blood pressure in hypovolemic shock such as occurs during hemorrage.