Nitric oxide

Class

Nitrite-based vasodilator

Notes

original target text: Nitric oxide pathway

Nitric oxide (NO) is a small, short-lived gaseous signaling molecule produced naturally by cells lining blood vessels. It diffuses into adjacent smooth muscle cells, where it activates an enzyme called soluble guanylate cyclase, raising levels of a second messenger, cyclic GMP. This cascade relaxes vascular smooth muscle, producing vasodilation, and also influences platelet activity and inflammatory signaling. Because NO synthesis is often impaired or overwhelmed in certain diseases, supplying it directly can restore vasodilator tone where the body's own production is inadequate. This mechanism is particularly relevant in conditions involving elevated pressure within the pulmonary circulation, where selective dilation of vessels supplying ventilated lung tissue improves oxygen delivery without lowering blood pressure throughout the body, since inhaled NO acts locally in the lungs and is rapidly inactivated once it enters the bloodstream. Because it is a gas, nitric oxide must be administered by inhalation, precisely dosed and monitored, and its use requires attention to potential toxic byproducts formed on exposure to oxygen. The pathway it engages is a fundamental piece of vascular physiology, making it relevant across multiple settings where regional blood flow or vascular tone needs to be adjusted without broad systemic effects.