Final answer:
The drug that causes vasodilation and is blocked by atropine is nitric oxide (NO).
Step-by-step explanation:
The drug that causes vasodilation and can be blocked by atropine is nitric oxide (NO).
Nitric oxide is a paracrine chemical that causes vasodilation by relaxing the smooth muscles of blood vessels. It acts as a signaling molecule, released by endothelial cells, and diffuses to the smooth muscle cells to induce relaxation.
Atropine is an anticholinergic drug that blocks muscarinic acetylcholine receptors. It does not directly block the vasodilation caused by nitric oxide, but it can block the effects of acetylcholine on blood vessels, which may indirectly modulate vasodilation.