c-AMP is a second messenger for all of the following, EXCEPT:

**Core Concept**
c-AMP (cyclic adenosine monophosphate) is a crucial second messenger in cellular signaling, playing a vital role in transmitting signals from hormones, neurotransmitters, and other extracellular molecules to intracellular targets. This process is essential for various physiological responses, including glycogenolysis, lipolysis, and vasodilation.

**Why the Correct Answer is Right**
c-AMP acts as a second messenger for various hormones and neurotransmitters, including glucagon, epinephrine (adrenaline), and dopamine. When these hormones bind to their respective receptors, they activate G-proteins, which in turn activate adenylate cyclase, leading to an increase in c-AMP levels within the cell. Elevated c-AMP levels activate protein kinase A (PKA), which phosphorylates and activates downstream targets, ultimately leading to the desired physiological response.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as c-AMP is not the primary second messenger for this hormone.
**Option B:** This option is incorrect as c-AMP is indeed a second messenger for this hormone, leading to glycogenolysis and gluconeogenesis.
**Option C:** This option is incorrect as c-AMP is indeed a second messenger for this hormone, leading to vasodilation and smooth muscle relaxation.

**Clinical Pearl / High-Yield Fact**
c-AMP plays a crucial role in the regulation of cellular metabolism, particularly in the context of glucose and lipid metabolism. Understanding the role of c-AMP is essential for appreciating the pathophysiology of various metabolic disorders, such as type 2 diabetes and insulin resistance.

**Correct Answer: D**