Val4-DDAVP can be used to prepare samples for qualitative detection of desmopressin in plasma by using liquid chromatography-electrospray tandem mass spectrometry. Val4-DDAVP is a V1 antagonist that stabilizes the cardiocirculatory function in normal human as well as in patients suffering from catecholamine-resistant vasodilatory shock. It can also stimulate three acid-base transporters and hence increases the capability of the cell to regulate pHi.Mpa-Tyr-Phe-Val-Asn-Cys-Pro-D-Arg-Gly-NH2 (Mpa1-Cys6) or Mpa-YFVNCPrG-NH2 (Mpa1-Cys6)