What Are Gasotransmitters and How They Signal in Your Body

Toxic Gases, Essential Messengers

Nitric oxide, carbon monoxide, and hydrogen sulfide are best known as poisons. Breathe enough of any one of them and you die. Yet every cell in the human body deliberately manufactures tiny quantities of these same gases and uses them to send messages that keep organs functioning. Scientists call them gasotransmitters—a class of signaling molecules that has rewritten textbook biology over the past three decades.

Unlike conventional neurotransmitters such as serotonin or dopamine, gasotransmitters cannot be stored in vesicles. They are produced on demand, diffuse freely through cell membranes without needing a receptor at the gate, and break down within seconds. That speed and permeability make them uniquely suited for rapid, short-range communication between and within cells.

The Big Three

Nitric Oxide (NO)

Nitric oxide was the first gasotransmitter recognized by science. In 1998, Robert Furchgott, Louis Ignarro, and Ferid Murad won the Nobel Prize in Physiology or Medicine for showing that NO relaxes blood vessel walls, lowering blood pressure. The discovery explained how nitroglycerin—prescribed for chest pain since the 1870s—actually works. Today, NO is known to regulate immune defense, wound healing, and neural communication. Enzymes called nitric oxide synthases (NOS) produce it from the amino acid L-arginine.

Carbon Monoxide (CO)

Carbon monoxide, the silent killer of faulty furnaces, is also generated inside every human body by the enzyme heme oxygenase, which breaks down old hemoglobin. At the minuscule concentrations cells produce, CO acts as an anti-inflammatory agent, helps regulate circadian rhythms, and protects tissues during organ transplantation. Because CO is chemically stable, it can travel farther than NO before degrading, making it effective for signaling across longer distances within tissue.

Hydrogen Sulfide (H₂S)

The newest member of the trio, hydrogen sulfide, smells like rotten eggs and is lethal in high doses. But at the nanomolar concentrations the body produces, H₂S relaxes smooth muscle, modulates inflammation, and plays a critical role in the brain. Two enzymes—cystathionine β-synthase (CBS) in the brain and cystathionine γ-lyase (CSE) in peripheral tissues—generate it from the amino acid cysteine.

How They Work at the Molecular Level

Each gasotransmitter signals through a different chemical trick. NO activates an enzyme called soluble guanylyl cyclase, which produces a second messenger molecule (cyclic GMP) that triggers downstream effects like blood vessel dilation. CO binds to iron-containing heme proteins, altering their activity. H₂S modifies proteins through a process called S-sulfhydration—attaching a sulfur atom to reactive cysteine residues on target proteins, which typically activates them.

According to a review in Nature Reviews Drug Discovery, all three gases can interact with one another's pathways, sometimes amplifying and sometimes opposing each other's effects—a level of crosstalk that researchers are still mapping.

Why They Matter for Medicine

Understanding gasotransmitters has already produced blockbuster drugs. Viagra (sildenafil) works by prolonging the NO signaling cascade. Inhaled NO is a standard therapy for newborns with pulmonary hypertension. Researchers are now developing slow-release H₂S donor drugs for conditions ranging from heart failure to inflammatory bowel disease.

Recent research from Johns Hopkins Medicine has highlighted H₂S's role in Alzheimer's disease. Scientists found that mice engineered to lack the CSE enzyme—and thus unable to produce normal levels of hydrogen sulfide—developed memory loss, DNA damage, and compromised blood-brain barriers, all hallmarks of Alzheimer's. The findings suggest that maintaining healthy H₂S levels in the brain may be protective against neurodegeneration.

What Comes Next

The biggest challenge is dosing. All three gases are toxic at high concentrations, so pharmaceutical companies are engineering molecules that release controlled amounts only where needed. Several H₂S-releasing compounds are already in clinical trials. Meanwhile, a handful of researchers argue that other small gases—such as sulfur dioxide and ammonia—may eventually join the gasotransmitter family, though the evidence remains preliminary.

What began as a paradox—poisons that heal—has become one of the most active frontiers in biomedical research. The gases your body makes to kill invaders and relay messages may soon be harnessed to treat diseases from hypertension to dementia.