Which second messenger is activated by the action of epinephrine binding to its receptor?

Epinephrine, also known as adrenaline, binds to adrenergic receptors on target cells, which are G protein-coupled receptors (GPCRs). This binding initiates a cascade of signal transduction within the cell. One of the key steps in this process is the activation of the enzyme adenylate cyclase.

When adenylate cyclase is activated, it catalyzes the conversion of ATP (adenosine triphosphate) to cAMP (cyclic adenosine monophosphate). cAMP acts as a second messenger within the cell, mediating a variety of physiological responses associated with the "fight or flight" response, such as increased heart rate and enhanced breakdown of glycogen to glucose.

The other options represent different signaling pathways. IP3 (inositol trisphosphate) and DAG (diacylglycerol) are products of phospholipase C activation and are involved in a different signaling pathway, often related to calcium signaling. cGMP (cyclic guanosine monophosphate) is another second messenger involved primarily in pathways such as vasodilation, typically through nitric oxide signaling, rather than the response to epinephrine.

Thus, cAMP is the correct second messenger