This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: A.N.S., Subject name: Pharmacology
Drug H is most like 
Select and explain. 
A. Epinephrine, B. Isoproterenol, C. Norepinephrine, D. Phenylephrine
A: Epinephrine
Answer: A: Epinephrine 
Explanation: The effects of Drug H are changed by treatment with either an alpha or beta blocker, so Drug H must have activity at both receptors (choices B, D, and E are ruled out). "Reversal" of a pressor effect can only occur if the drug has beta2 activity (choice C is ruled out). Drug H is epinephrine.