Final answer:
Endothelial cells produce Nitric Oxide (NO), which is a vasodilator that induces relaxation of smooth muscles and vasodilation. Endothelins, not being vasodilators, are vasoconstrictors and affect blood pressure differently. PDE5 inhibitors, like sildenafil, are used to promote vasodilation for treating certain conditions.
Step-by-step explanation:
Nitric Oxide: A Major Vasodilator
Endothelial cells produce a known vasodilator called Nitric Oxide (NO). It is a gas that acts as a ligand and plays a crucial role in blood flow regulation by causing vasodilation - the widening of blood vessels. Nitric oxide diffuses across the plasma membrane, interacts with receptors in smooth muscle, and induces tissue relaxation. With a very short half-life, its effects are localized and rapid. This vasodilator is also relevant in medical treatments such as nitroglycerin and prescription medications for erectile dysfunction, such as Viagra.
In contrast, endothelins are 21-amino acid peptides which are potent vasoconstrictors, typically not influencing blood pressure in healthy individuals but can have adverse effects in conditions such as diabetic kidney disease by causing sodium retention and damaging podocytes. They are produced in various cells including endothelial cells, but they are not considered vasodilators.
For the treatment of conditions like erectile dysfunction, phosphodiesterase type 5 inhibitors (PDE5 inhibitors) like sildenafil have been developed that can inhibit the enzyme responsible for reversing vasodilation, hence promoting increased blood flow and vasodilation.