Epinephrine is a catecholamine, a sympathomimetic monoamine derived from the amino acids phenylalanine and tyrosine.
Epinephrine plays a central role in the short-term stress reaction the physiological response to threatening, exciting or environmental stressor conditions such as high noise levels or bright light (see fight-or-flight response). It is secreted by the adrenal medulla. When released into the bloodstream, epinephrine binds to multiple receptors and has numerous effects throughout the body. It increases heart rate and stroke volume, dilates the pupils, and constricts arterioles in the skin and gut while dilating arterioles in leg muscles. It elevates the blood sugar level by increasing hydrolysis of glycogen to glucose in the liver, and at the same time begins the breakdown of lipids in fat cells. Epinephrine has a suppressive effect on the adaptive immune system.