Which Observation Suggested the Involvement of a Second Messenger in Epinephrine's

Multiple Choice

Which observation suggested the involvement of a second messenger in epinephrine's effect on liver cells?

A) Enzymatic activity was proportional to the amount of calcium added to a cell-free extract.
B) Receptor studies indicated that epinephrine was a ligand.
C) Glycogen breakdown was observed only when epinephrine was administered to intact cells.
D) Glycogen breakdown was observed when epinephrine and glycogen phosphorylase were combined.
E) Epinephrine was known to have different effects on different types of cells.