Called epinephrine in the U.S., this is a substance secreted into the bloodstream and reacted to by specialised receptors throughout the body, initiating a "code blue" or flight-or-fight response. Many receptors are a regular part of sympathetic function, and respond to their own local relative, norepinephrine or noradrenalin, in the course of normal autonomic nervous system interplay. See: SYMPATHETIC, PARASYMPATHETIC, LIMBIC