The amino acid which on decarboxylation gives rise to a product with potent vasodilator propeies is:

Histamine is derived from the decarboxylation of the aminoacid histidine, a reaction catalyzed by the enzyme L-histidine decarboxylase present in the liver. It is a hydrophilic vasoactive amine. Ref: Neuroscience in Medicine edited by P. Michael Conn, Page 496