Which of the following hormones does not act by a second messenger system ?

Options

A. Glucagon
B. Epinephrine
C. LH
D. Aldosterone

Answer

To solve the question "Which of the following hormones does not act by a second messenger system?", we will analyze the options provided and understand the mechanisms of action for each hormone mentioned.

### Step-by-Step Solution:

1. **Understand the Second Messenger System**:
- The second messenger system is a mechanism through which certain hormones (primarily protein-based hormones) exert their effects on target cells. These hormones bind to receptors on the cell surface, leading to the activation of a second messenger inside the cell, which then triggers a series of cellular responses.

2. **Identify the Nature of Hormones**:
- Hormones can be classified into two main categories: protein (or peptide) hormones and steroid hormones.
- Protein hormones (e.g., insulin, glucagon, epinephrine) generally act through second messenger systems.
- Steroid hormones (e.g., aldosterone) typically pass through the cell membrane and bind to intracellular receptors, thus not requiring a second messenger.

3. **Analyze Each Option**:
- **Option 1: Glucagon**: This is a protein hormone that acts through a second messenger system (cAMP).
- **Option 2: Epinephrine**: This is also a protein hormone that utilizes a second messenger system (cAMP).
- **Option 3: Luteinizing Hormone (LH)**: This is a protein hormone that acts via a second messenger system (cAMP).
- **Option 4: Aldosterone**: This is a steroid hormone that does not act through a second messenger system. Instead, it binds to intracellular receptors.

4. **Conclusion**:
- Based on the analysis, the hormone that does not act by a second messenger system is **Aldosterone**.

### Final Answer:
**Aldosterone** does not act by a second messenger system.

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