## Core Concept
The question tests the understanding of second messenger systems in cellular signaling, specifically focusing on c-AMP (cyclic adenosine monophosphate). c-AMP is a crucial second messenger in cellular signal transduction pathways, acting downstream of various G protein-coupled receptors (GPCRs).

## Why the Correct Answer is Right
The correct answer utilizes a different second messenger system. While c-AMP is involved in signaling pathways for many hormones and neurotransmitters, some receptors and ligands use alternative second messengers, such as IP3 (inositol trisphosphate) and DAG (diacylglycerol), which are associated with Gq protein-coupled receptors.

## Why Each Wrong Option is Incorrect
- **Option A:** This option is incorrect because it uses c-AMP as a second messenger. An example of such a receptor is the beta-adrenergic receptor, which activates Gs proteins, leading to an increase in c-AMP levels.
- **Option B:** This option also uses c-AMP as a second messenger. For instance, the glucagon receptor activates adenylate cyclase via Gs proteins, increasing c-AMP.
- **Option C:** Similarly, this option involves c-AMP in its signaling pathway. The ACTH (adrenocorticotropic hormone) receptor is another example that signals through c-AMP.

## Why Option D is Correct but Explained Here for Context
- **Option D:** This option does not use c-AMP as its second messenger. Instead, it acts through a different pathway, often involving IP3 and DAG as second messengers, which are produced from PIP2 by the action of phospholipase C (PLC), typically activated by Gq-coupled receptors.

## Clinical Pearl / High-Yield Fact
A key point to remember is that the **vasopressin (V1) receptor** primarily signals through the **Gq protein**, leading to the production of **IP3 and DAG** as second messengers, not c-AMP. This is crucial for understanding how different hormones and neurotransmitters exert their effects on cells.

## Correct Answer: D. Vasopressin (V1) receptor.