Vasopressin

A 9-amino-acid neuropeptide hormone synthesized in the hypothalamus. Primary functions include increasing water reabsorption in the kidneys (antidiuretic effect) and vasoconstriction. Also acts as a neuropeptide in the brain modulating social behavior, pair bonding, and stress response — complementary to oxytocin. Relevant context for intranasal neuropeptide delivery research.