PDE5A
PDE5A phosphodiesterase 5A — the molecular target that 1 compounds in the wiki act on.
In one line: The enzyme that ends the "widen blood vessels" signal — Viagra-type drugs block it.
PDE5A breaks down the messenger that keeps blood vessels relaxed and open. Erectile-dysfunction drugs (sildenafil, tadalafil) block this enzyme, so the "stay widened" signal lasts longer and blood flow is maintained where it's needed. Daily low-dose tadalafil is also studied for broader blood-vessel and prostate benefits.
Important safety point: never combine these with nitrates or high-dose beetroot — together they can drop blood pressure dangerously.