Final answer:
Nitric oxide (NO) causes vasodilation by interacting with receptors in smooth muscle, inducing relaxation and causing blood vessels to dilate.
Step-by-step explanation:
Nitric oxide (NO) causes vasodilation. NO is a gas that acts as a ligand and diffuses directly across the plasma membrane. It interacts with receptors in smooth muscle, inducing relaxation and causing blood vessels to dilate. Nitroglycerin triggers the release of NO, which restores blood flow to the heart. NO is also targeted by prescription medications for erectile dysfunction, promoting the vasodilation necessary for an erection.