Epinephrine and norepinephrine are chemically similar compounds that are involved in the body’s fight or flight response to stress. The key difference between these chemicals is in their structure; norepinephrine contains a hydrogen atom whereas epinephrine has a methyl group. This structural difference allows them to act in slightly different ways as they connect to receptors in the muscles and nervous system. Also known as adrenalin and noradrenaline, these chemicals act on adrenergic receptors throughout the body.
Norepinephrine is secreted by certain neurons in the brain as well as the adrenal gland, while epinephrine is produced only in the adrenal gland. One of the important differences between epinephrine and norepinephrine is that norepinephrine can act as a psychoactive compound in the brain, while its derivative, epinephrine, does not. When people experience physical and emotional stress, the adrenal gland pumps out both hormones to prepare for a response.
Increased levels of epinephrine contribute to the constriction of blood vessels to raise blood flow. Norepinephrine promotes circulation of blood to the skeletal muscle to provide these muscles with nutrients to fuel a short energy burst. Epinephrine can increase the production of energy by the body using compounds like glucose released in response to rising norepinephrine levels. This compound also relaxes the smooth muscle in the airways to dilate the bronchial tubes, increasing oxygen intake.
Adrenergic receptors all over the body respond when these hormones, which can also act as neurotransmitters, are released. A cascade of reactions occurs as epinephrine and norepinephrine levels rise, until the crisis is over and the release of the chemicals slows. During this period, people may feel giddy or excited because of the increased oxygenation and blood flow. This can also mask symptoms of injuries or strains, an evolutionary adaptation to allow humans to escape from dangerous situations and reach safety even when injured.
Medically, both epinephrine and norepinephrine are used in a variety of procedures, particularly with patients who are in severe medical distress. Patients with allergies, for example, may carry epinephrine to treat severe allergic reactions and keep their airways open until they can get help. These medications can also be used as stimulants in patients experiencing cardiac problems. Norepinephrine is sometimes used in the treatment of depression and other mental health conditions because it acts on the brain. Administration of epinephrine and norepinephrine must be done with care, as these chemicals are powerful and can create complications if used in excess.