Which of the following decreases the heart beat?

Options

A. Epinephrine
B. Norepinephrine
C. Thyroxine
D. Acetylcholine

Answer

To determine which of the following options decreases the heart rate, we will analyze each option provided:

1. **Epinephrine**:
- Epinephrine is a hormone produced by the adrenal glands. It is commonly known as adrenaline.
- Its primary function is to prepare the body for 'fight or flight' responses, which includes increasing heart rate, enhancing muscle strength, and boosting energy supplies.
- Therefore, epinephrine does **not** decrease heart rate.

2. **Norepinephrine**:
- Norepinephrine is also a hormone and neurotransmitter that plays a role in the body's response to stress.
- Similar to epinephrine, norepinephrine increases heart rate and blood pressure.
- Hence, norepinephrine does **not** decrease heart rate.

3. **Thyroxine**:
- Thyroxine (T4) is a hormone produced by the thyroid gland.
- It regulates metabolism and influences heart rate. Thyroxine generally increases heart rate and metabolic activity.
- Therefore, thyroxine does **not** decrease heart rate.

4. **Acetylcholine**:
- Acetylcholine is a neurotransmitter that plays a crucial role in the parasympathetic nervous system.
- It is responsible for slowing down the heart rate by acting on the heart's pacemaker cells and promoting slower contractions.
- Thus, acetylcholine is the compound that decreases heart rate.

**Conclusion**: The correct answer is **acetylcholine**, as it is the only option that decreases the heart rate.

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