Which one of the following is not a second messenger in hormone action

Options

A. cGMP
B. Calcium
C. Sodium
D. cAMP

Answer

To determine which of the following options is not a second messenger in hormone action, we need to analyze the given options: cGMP, Calcium, Sodium, and cAMP.

### Step-by-Step Solution:

1. **Understanding Second Messengers**:
- Second messengers are molecules that relay signals received at receptors on the cell surface to target molecules inside the cell, thereby amplifying the strength of the signal. Common second messengers include cyclic AMP (cAMP), cyclic GMP (cGMP), and calcium ions.

2. **Identifying the Options**:
- **cAMP (Cyclic Adenosine Monophosphate)**: This is a well-known second messenger that is involved in various signaling pathways, particularly those activated by hormones like adrenaline.
- **cGMP (Cyclic Guanosine Monophosphate)**: Similar to cAMP, cGMP is also a second messenger that plays a role in signaling pathways, particularly in smooth muscle relaxation.
- **Calcium**: Calcium ions act as a second messenger in many signaling pathways, including muscle contraction and neurotransmitter release.
- **Sodium**: Sodium is primarily an electrolyte that helps in maintaining membrane potential and is not typically classified as a second messenger in hormone action.

3. **Conclusion**:
- Among the options provided, Sodium is the only one that is not considered a second messenger in hormone action. Therefore, the correct answer is **Sodium**.

### Final Answer:
**Sodium** is not a second messenger in hormone action.

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