Norepinephrine
Overview
Norepinephrine (NE), also known as noradrenaline (NA), is a catecholamine with multiple roles including as a hormone and a neurotransmitter. As part of the body's response to stress, norepinephrine affects the way the brain pays attention and responds to events. It is also involved in the body's "fight or flight" response, which prepares the body for action.
Biosynthesis
Norepinephrine is synthesized from tyrosine, an amino acid which is derived from dietary protein. The biosynthesis of norepinephrine involves a series of enzymatic reactions. The first step is the conversion of tyrosine to DOPA by the enzyme tyrosine hydroxylase. DOPA is then converted to dopamine by the enzyme DOPA decarboxylase. Finally, dopamine is converted to norepinephrine by the enzyme dopamine β-hydroxylase.
Function
Norepinephrine functions both as a neurotransmitter and a hormone. As a neurotransmitter, it is released from the sympathetic nervous system to transmit signals between nerve cells in the brain and spinal cord. As a hormone, it is released into the bloodstream by the adrenal medulla and affects various organs throughout the body.
Role in the Body
Norepinephrine plays a pivotal role in the body's response to stress and is involved in a variety of physiological processes. These include increasing heart rate and blood pressure, dilating pupils, widening air passages allowing for greater oxygen flow to the muscles, and slowing digestion.
Clinical Significance
Abnormal levels of norepinephrine in the brain can contribute to a variety of mental health disorders, including depression, anxiety, and post-traumatic stress disorder. Certain medications, such as selective serotonin reuptake inhibitors (SSRIs), can help to regulate the amount of norepinephrine in the brain and alleviate these conditions.