histamine

noun1

1. •
   An amine, C₅H₉N₃, formed by decarboxylation of histidine, that causes dilatation of capillaries, contraction of smooth muscle, and stimulation of gastric acid secretion; it is released during allergic reactions.

   • Mellanby and Twort have isolated from the faeces a bacillus which is able to produce from one of the amino acids normally formed in digestion of proteins a highly active body, histamine. — 1913