In the regulation of the anterior pituitary, which hypothalamic hormone can act as both a releasing hormone and an inhibiting hormone depending on the target pituitary cell type?

• A. Thyrotropin-releasing hormone (TRH)
• B. Dopamine (prolactin-inhibiting hormone)
• C. Thyrotropin-releasing hormone (TRH) and gonadotropin-releasing hormone (GnRH)
• D. Gonadotropin-releasing hormone (GnRH)

Answer: (C)

Verified step by step guidance

1. Step 1: Understand the role of the hypothalamus in regulating the anterior pituitary. The hypothalamus secretes hormones that either stimulate (releasing hormones) or inhibit (inhibiting hormones) the secretion of anterior pituitary hormones.
2. Step 2: Identify the hormones mentioned: Thyrotropin-releasing hormone (TRH), Dopamine (prolactin-inhibiting hormone), and Gonadotropin-releasing hormone (GnRH). Each has specific target cells in the anterior pituitary and distinct effects.
3. Step 3: Recognize that TRH primarily stimulates the release of thyroid-stimulating hormone (TSH) from the anterior pituitary, but it can also stimulate prolactin release, showing dual action depending on the target cell type.
4. Step 4: Note that dopamine mainly acts as an inhibiting hormone for prolactin secretion, and GnRH primarily stimulates the release of luteinizing hormone (LH) and follicle-stimulating hormone (FSH), without known inhibitory effects.
5. Step 5: Conclude that the hypothalamic hormone capable of acting as both a releasing and inhibiting hormone depending on the anterior pituitary target cell is Thyrotropin-releasing hormone (TRH), due to its dual stimulatory effects on different cell types.