Histamine
A substance normally "stored" in specialised cells (called mast cells) from where it is released by specific stimuli. Histamine again stimulates excretion from glands, influences blood pressure, digestion, cell membrane permeability (and thus fluid content of cells) and other body functions. Normally release of histamine is a well controlled process, but sometimes huge amounts of histamine can be released in an uncontrolled way, e.g. in allergies, where usually some foreign substance triggers symptoms like sneezing, coughing, asthma, excessive production of mucus in the airways, itching/rashes etc. Contrast media can also cause such uncontrolled release of histamine leading to reactions very similar to allergies, although the mechanism behind these reactions is different. Some contrast media are much more likely than others to cause such uncontrolled release of histamine, and therefore release of histamine from isolated cultures of mast cells is one of several indicators of chemotoxicity. Non-ionic contrast media cause less histamine release than ionic CM.
GE Healthcare Glossary