It is a cleavage product (formed by splitting of a compound molecule into a simpler one) of preprooxyphysin.
[1] It is a neurohypophysial hormone that is transported in vesicles with oxytocin, the other cleavage product, along axons, from magnocellular neurons of the hypothalamus to the posterior lobe of the pituitary.
It is produced in the cell bodies of the paraventricular and supraoptic nuclei and transported to its site of release in the axon terminals of the posterior pituitary.
[2] Vasopressin, a hormone similar in structure to oxytocin, is analogously bound and transported by Neurophysin II.
Both Ile and Phe are hydrophobic amino acids and undergo analogous binding to neurophysins.