Which of these pairs of hormones are not antagonistic in their action ?

Options

A. Erythropoiesis : Tyroxine and Erythropoietin
B. Calcium metabolism : Parathormone and Calcitonin
C. Glucose metabolism : Insulin and Glucagon
D. Blood pressure regulation : Aldosterone and Atrial Natriuretic Factor

Answer

To determine which pair of hormones are not antagonistic in their action, we need to analyze the functions of the hormones provided in the options.

### Step-by-Step Solution:

1. **Understand Antagonistic Hormones**: Antagonistic hormones are those that have opposing effects on the same physiological process. For example, if one hormone increases a certain level (like blood sugar), the antagonistic hormone will decrease it.

2. **Identify the Hormones**:
- **Erythropoietin (EPO)**: This hormone is produced by the kidneys and stimulates the production of red blood cells (RBCs) in the bone marrow.
- **Thyroxine (T4)**: This hormone is produced by the thyroid gland and regulates metabolism, but it also plays a role in the maturation of red blood cells.

3. **Analyze the Actions of Erythropoietin and Thyroxine**:
- Both Erythropoietin and Thyroxine contribute to the process of erythropoiesis (the formation of red blood cells). They do not have opposing actions; instead, they work together to enhance RBC production.

4. **Examine Other Hormonal Pairs**:
- **Parathyroid Hormone (PTH) and Calcitonin**: PTH increases blood calcium levels, while Calcitonin decreases them. These hormones are antagonistic.
- **Insulin and Glucagon**: Insulin decreases blood sugar levels, while Glucagon increases them. These hormones are also antagonistic.
- **Aldosterone and Arterial Natriuretic Factor (ANF)**: Aldosterone increases blood pressure by promoting sodium retention, while ANF decreases blood pressure by promoting sodium excretion. These hormones are antagonistic as well.

5. **Conclusion**: The only pair of hormones that are not antagonistic in their action is **Erythropoietin and Thyroxine**, as both support the process of red blood cell formation.

### Final Answer:
The pair of hormones that are not antagonistic in their action is **Erythropoietin and Thyroxine**.