All of the following are obligate coronary vasodilators except:: (A) Nitroglycerine, (B) Nitric oxide, (C) Hypoxia and Hypercapnia, (D) Acetylcholine
Answer is D. 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.