May 04, 2020
Blame me when your hair turns gray.
What molecule am I?
Image of Norepinephrine 3D Image of Norepinephrine

Norepinephrine is a natural compound in the catecholamine family that acts as a hormone and neurotransmitter. Its original name was noradrenaline, which is still used in the United Kingdom. The United States and the World Health Organization use norepinephrine. “Nor” in norepinephrine indicates that it has the structure of the parent molecule epinephrine with a hydrogen atom in place of the N-methyl group.

According to the Merck Index, norepinephrine “occurs in animals and [humans] and is a sympathomimetic hormone of both adrenal origin and adrenergic orthosympathetic postganglionic origin in [humans].” As an adrenal hormone, its release triggers vasoconstriction, which increases blood pressure. Despite its hazards (see table), this characteristic led scientists to develop norepinephrine as an intravenous drug for treating patients with very low blood pressure.

Physiologist Ulf van Euler at the Karolinska Institute (Solna, Sweden) discovered norepinephrine’s role in the body in 1945. He shared the 1970 Nobel Prize in Physiology or Medicine for his work on neurotransmitters.

Earlier this year, researchers reported a previously unknown property of norepinephrine. Ya-Chieh Hsu and colleagues at Harvard University (Cambridge, MA) and other research institutions used laboratory mice to determine the underlying biochemical cause of stress-induced hair depigmentation. They found that the culprit is norepinephrine, which is released by mammals’ adrenal glands when animals are under stress.

But the authors’ big surprise came when they removed the adrenal glands from mice to test their finding: The rodents still went gray. Undaunted, the researchers discovered that animals under stress also release norepinephrine from the sympathetic nervous system. The chemical reaches hair follicles and depletes them of pigment-producing stem cells.

Norepinephrine hazard information

Hazard class*Hazard statement
Acute toxicity, oral, category 2H300—Fatal if swallowedChemical Safety Warning
Acute toxicity, dermal, category 2H310—Fatal in contact with skinChemical Safety Warning
Acute toxicity, inhalation, category 1H330—Fatal if inhaledChemical Safety Warning

*Globally Harmonized System of Classification and Labeling of Chemicals. Explanation of pictograms.

Norepinephrine fast facts

CAS Reg. No.51-41-2
1,2-Benzenediol, 4-[(1R)-2-amino-1-hydroxyethyl]-
Empirical formulaC8H11NO3
Molar mass169.18 g/mol
AppearanceOff-white to tan crystals; colorless microcrystals
Melting point217 ºC (dec)
Water solubility0.85 g/L

MOTW Update

Ethylene oxide was the Molecule of the Week for November 18, 2019. It is used extensively in chemical manufacturing, agriculture, and fumigation, but it is extremely hazardous. In March 2020, the US Environmental Protection Agency’s Office of the Inspector General found that the agency had not done enough to inform people who are living near ethylene oxide–emitting chemical plants that they are likely to have an increased risk of cancer. The OIG even recommended that EPA use unverified data to warn neighbors of the hazard.

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