Final answer:
Nitric Oxide (NO) is the first direct acting vasodilator discussed. It acts as a ligand by diffusing directly across the plasma membrane and stimulating the relaxation of smooth muscle in blood vessels, leading to their dilation. Nitroglycerin is a medication that triggers the release of NO, promoting the dilation of blood vessels and improving blood flow.
Step-by-step explanation:
The first direct acting vasodilator we will discuss is Nitric Oxide (NO). NO is a gas that acts as a ligand by diffusing directly across the plasma membrane and interacting with receptors in smooth muscle to induce relaxation. One of its roles is to cause blood vessels to dilate, which increases blood flow. Nitroglycerin, a treatment for heart disease, triggers the release of NO, resulting in the dilation of blood vessels and restoration of blood flow to the heart.