All of the following are obligate coronary vasodilators except:
All are known to cause vasodilatation.
Only acetylcholine can also be a vasoconstrictor if the endothelium is dysfunctional or absent and nitric oxide can not be produced. In that case it is not an obligate vasodilator.
Nitroglycerine
Nitric oxide
Hypoxia and Hypercapnia
Acetylcholine