Endothelium-derived relaxing factor
Endothelium-derived relaxing factor (EDRF) is produced and released by the endothelium
The endothelium is the thin layer of cells that lines the interior surface of blood vessels, forming an interface between circulating blood in the lumen and the rest of the vessel wall. These cells are called endothelial cells. Endothelial cells line the entire circulatory system, from the heart...

 to promote smooth muscle relaxation. The best-characterized is nitric oxide
Nitric oxide
Nitric oxide, also known as nitrogen monoxide, is a diatomic molecule with chemical formula NO. It is a free radical and is an important intermediate in the chemical industry...

 (NO). Some sources equate EDRF and nitric oxide.

It is released in response to a variety of chemical and physical stimuli. It causes the smooth muscle
Smooth muscle
Smooth muscle is an involuntary non-striated muscle. It is divided into two sub-groups; the single-unit and multiunit smooth muscle. Within single-unit smooth muscle tissues, the autonomic nervous system innervates a single cell within a sheet or bundle and the action potential is propagated by...

 in the vessel wall to relax.

EDRF was discovered and characterized by Robert F. Furchgott
Robert F. Furchgott
Robert Francis Furchgott was a Nobel Prize-winning American biochemist.Furchgott was born in Charleston, SC, to Arthur Furchgott and Pena Sorentrue Furchgott...

, a winner of the Nobel Prize in Medicine in 1998 with his co-researchers Louis J. Ignarro and Ferid Murad
Ferid Murad
Ferid Murad is an Albanian-American physician and pharmacologist, and a co-winner of the 1998 Nobel Prize in Physiology or Medicine. He is also an honorary member of the Academy of Sciences and Arts of Kosovo.- Life :...


According to Furchgott's website at SUNY Downstate Medical Center
SUNY Downstate Medical Center
The State University of New York Health Science Center at Brooklyn, better known as SUNY Downstate Medical Center, is a public university and medical center located in central Brooklyn, New York and the only academic center for health education, research, and patient care serving Brooklyn’s 2.5...

, "...we are investigating whether the endothelium-derived relaxing factor (EDRF) is simply nitric oxide or a mixture of substances".

Although there is strong evidence that nitric oxide elicits vasodilation, there is some evidence tying this effect to neuronal rather than endothelial reactions.


According to some sources, EDRF refers not only to nitric oxide but also to other substances. Endothelium actually produces a number of endothelial-derived relaxing factors such as:
  • prostacyclin
    Prostacyclin is a member of the family of lipid molecules known as eicosanoids.As a drug, it is also known as "epoprostenol". The terms are sometimes used interchangeably.-History:...

  • Endothelium-derived hyperpolarizing factor, or EDHF (There is some evidence to suggest that EDHF is potassium
    Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...

  • Heme proteins from blood, which can also stimulate the inducible isoform of Heme oxygenase
    Heme oxygenase
    This reaction can occur in virtually every cell; the classic example is the formation of a bruise, which goes through different colors as it gradually heals: red heme to green biliverdin to yellow bilirubin...

     (HO-1, also known as heat shock protein 32), which produces Carbon monoxide
    Carbon monoxide
    Carbon monoxide , also called carbonous oxide, is a colorless, odorless, and tasteless gas that is slightly lighter than air. It is highly toxic to humans and animals in higher quantities, although it is also produced in normal animal metabolism in low quantities, and is thought to have some normal...

    , which can relax smooth muscle.

Older candidate molecules include nitroxyl
Nitroxyl is the chemical compound HNO. It is well known in the gas phase . In aqueous solution it acts as an acid with the conjugate base NO−, . NO− is the reduced form of nitric oxide and is isoelectronic with dioxygen...

 and hydroxylamine
Hydroxylamine is an inorganic compound with the formula NH2OH. The pure material is a white, unstable crystalline, hygroscopic compound. However, hydroxylamine is almost always provided and used as an aqueous solution. It is used to prepare oximes, an important functional group. It is also an...


The endothelium also produces a number of vasoconstricting agents, and there is a balance of constricting and relaxing signals.
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