- a heterocyclic amine, C5H9N3, released by mast cells when tissue is injured or in allergic and inflammatory reactions, causing dilation of small blood vessels and smooth muscle contraction.
- a commercial form of this compound, obtained from histidine and used chiefly in the diagnosis of gastric and circulatory functions.
- an amine formed from histidine and released by the body tissues in allergic reactions, causing irritation. It also stimulates gastric secretions, dilates blood vessels, and contracts smooth muscle. Formula: C 5 H 9 N 3
