Norepinephrine, also known as norepinephrine, is a hormone and neurotransmitter with the molecular formula C8H11NO3. It is a component of the autonomic nervous system and has stimulating, invigorating effects, which is why it has many uses as a drug. Both overproduction and underproduction of norepinephrine can have far-reaching effects on the organism.
What is norepinephrine?
Schematic diagram showing the anatomy and structure of the endocrine (hormone) system. Click to enlarge. Norepinephrine is an important hormone of the human organism, that is, a biochemical messenger that has a regulating or stimulating effect on certain organs. At the same time, norepinephrine is also a neurotransmitter, i.e. a neuronal messenger involved in the transmission of excitation at the synapses of nerve cells. This occurs through the transmission of electrical impulses, so-called action potentials. Norepinephrine is a component of the autonomic nervous system and is therefore involved in numerous vital functions such as blood pressure, respiration and metabolism. It is assigned to the substance class of catecholamines. This class of amino acid derivatives is formed from the amino acids tyrosine and phenylalanine. Other important hormones in this substance class are adrenaline and dopamine. Dopamine is the precursor of norepinephrine. Norepinephrine differs from epinephrine only in the absence of a methyl group on the amino group. For this reason, norepinephrine is also called demethylated epinephrine. Stereochemically, norepinephrine occurs naturally as L-minus norepinephrine.
Production, formation, and manufacture
The formation of norepinephrine as a hormone occurs mainly in the medulla of the adrenal gland, a paired endocrine gland. Here, noradrenogenic neurons and chromaffin cells are found whose function is to synthesize norepinephrine. In its function as a neurotransmitter, noradrenaline is primarily secreted by specific neurons. These neurons are located in the sympathetic nervous system and in specific areas of the brain, such as the locus caeruleus. Precursors of noradrenalin are the amino acids tyrosine and phenylalanine. The synthesis of noradrenaline requires vitamin C, vitamin B6, magnesium and copper, which serve as electron donors and cofactors, among other things. The immediate precursor of norepinephrine is dopamine. This is oxidized by the enzyme dopamine-beta-hydroxylase, thus donating an electron, resulting in norepinephrine.
Function, action, and properties
The hormone norepinephrine belongs to the sympathetic nervous system, which makes up part of the autonomic nervous system. Basic function of the sympathetic nervous system is an increase in the performance of the organism in the presence of danger, effort or stress. Outside of dangerous situations, norepinephrine has an important function in increasing attention, motivation and mental performance. The mode of action of the sympathetic nervous system is also known as ergotropic. This means that the outwardly directed power of action of the body is increased. The sudden release of norepinephrine into the blood thus stimulates what is known as a fight-or-flight response. Stimulation of alpha-1 receptors and beta-1 receptors of the heart muscle increases blood pressure, causing the concentration of the hormone in the blood to rise rapidly. Following its property as a neurotransmitter, norepinephrine activates certain receptors called adrenoceptors. These are located on the arterioles. These are small arteries that merge into capillaries and are constricted by this activation. As a result, the muscles are strongly supplied with blood, so that reaction speed and performance increase. Because of its blood pressure-increasing effect, adrenaline is therefore used as an emergency medication in trauma and shock therapy. Its constricting effect on arterioles and capillaries is also used medically. For example, norepinephrine is added to local anesthetics to minimize bleeding and prevent the drug from entering the bloodstream.
Diseases, ailments, and disorders
Prolonged exposure to stress can lead to abnormally increased release of norepinephrine. One of the side effects triggered by norepinephrine may be suppression of the immune system.If the level is permanently elevated, inflammation can therefore be favored because the immune system is weakened. However, long-term overproduction of norepinephrine is unsustainable for the organism, which is why norepinephrine deficiency can eventually occur as a reaction to overproduction. This is considered a common cause of depression, which is why norepinephrine is found as a component in many antidepressants. Other possible side effects of increased production of norepinephrine can be organ damage and necrosis, because the narrowing of the arterioles results in poorer blood supply to organs and trades. For this reason, increased levels can also lead to heart failure. An abnormally elevated level of norepinephrine in the blood can also be an indication of various tumors of the adrenal gland or the brain. When determining the concentration in the blood, it is important that the needle is inserted at least thirty minutes before the blood sample is taken, as the insertion itself raises the norepinephrine level. Too low a concentration of norepinephrine, on the other hand, is found mainly in diseases of the adrenal glands, especially dysfunction, except in depression.
