Nitric oxide causes relaxation of vascular smooth muscle cells, resulting in increased blood flow and reduced vascular resistance.

Study: Contribution of nitric oxide to metabolic coronary vasodilation in the human heart.

When scientists blocked nitric oxide in people’s heart blood vessels, the vessels tightened up and blood flow decreased — proving that nitric oxide normally helps blood vessels relax so more blood can flow through.

Study: After 130 years, the molecular mechanism of action of nitroglycerin is revealed

This study figured out how a medicine called nitroglycerin turns into nitric oxide in the body, and nitric oxide is what makes blood vessels widen to improve blood flow. So yes, it helps explain how the medicine works.

Study: Downregulation of the α1- and β1-subunit of sGC in Arterial Smooth Muscle Cells of OPSCC Is HPV-Independent

This study shows that nitric oxide helps blood vessels relax by activating a special protein inside vessel walls. When that protein is damaged or reduced, the vessels can’t relax as well — which means nitric oxide’s job is to make blood vessels wider so blood can flow more easily.

Study: The biological lifetime of nitric oxide: implications for the perivascular dynamics of NO and O2.

This study shows that nitric oxide stays active near blood vessels long enough to help relax their walls, which lets more blood flow through — helping explain how it lowers blood pressure.