Which of these hormones is not secreted into the hypothalamohypophysial portal system ?

Options

A. PIH
B. ADH
C. GHRH
D. GnRH

Answer

To determine which hormone is not secreted into the hypothalamo-hypophysial portal system, we need to analyze the options provided:

1. **Understanding the Hypothalamo-Hypophysial Portal System**:
- This system is a network of blood vessels that directly connects the hypothalamus to the anterior pituitary gland. Hormones secreted by the hypothalamus travel through this portal system to influence the secretion of hormones from the anterior pituitary.

2. **Analyzing the Options**:
- **PIH (Prolactin Inhibiting Hormone)**: This hormone is secreted by the hypothalamus and travels through the portal system to inhibit the secretion of prolactin from the anterior pituitary. Therefore, it is secreted into the portal system.

- **ADH (Antidiuretic Hormone)**: This hormone, also known as vasopressin, is produced in the hypothalamus but is released from the posterior pituitary gland. It does not travel through the hypothalamo-hypophysial portal system, as it is not secreted into the anterior pituitary.

- **GHRH (Growth Hormone Releasing Hormone)**: This hormone stimulates the secretion of growth hormone from the anterior pituitary and is secreted into the portal system.

- **GnRH (Gonadotropin Releasing Hormone)**: This hormone stimulates the secretion of FSH and LH from the anterior pituitary and is also secreted into the portal system.

3. **Conclusion**:
- The hormone that is not secreted into the hypothalamo-hypophysial portal system is **ADH (Antidiuretic Hormone)**.

### Final Answer:
**ADH (Antidiuretic Hormone)** is not secreted into the hypothalamo-hypophysial portal system.

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