Question
Following hypothalamic ablation, the level of which of the following hormones is most likely to increase?
| A. | Growth Hormone (GH) |
| B. | Prolactin |
| C. |
Follicle-Stimulating Hormone (FSH) |
| D. |
Adrenocorticotropic Hormone (ACTH) |
|
Correct Answer � B Explanation |
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The hypothalamus regulates the anterior pituitary (adenohypophysis) through both stimulatory and inhibitory hormonal signals delivered via the hypophyseal portal system. Among these hormones:
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Most anterior pituitary hormones are under positive regulation by hypothalamic releasing hormones.
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Prolactin, however, is unique because its secretion is primarily under inhibitory control by dopamine (also called prolactin-inhibiting factor, PIF).
After Hypothalamic Ablation:
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Dopamine secretion is lost, removing the inhibitory tone on lactotrophs (prolactin-secreting cells) in the anterior pituitary.
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As a result, prolactin secretion increases.
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Conversely, other pituitary hormones like GH, ACTH, and FSH tend to decrease due to loss of their respective hypothalamic releasing hormones (GHRH, CRH, GnRH).
Why Other Options Are Incorrect
A. Growth Hormone (GH):
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GH secretion is controlled by:
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GHRH (stimulatory)
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Somatostatin (inhibitory)
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Hypothalamic ablation removes both, but loss of GHRH leads to a net decrease in GH secretion.
C. Follicle-Stimulating Hormone (FSH):
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Requires GnRH for stimulation.
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Ablation of hypothalamus stops GnRH release → FSH falls.
D. Adrenocorticotropic Hormone (ACTH):
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Stimulated by CRH from the hypothalamus.
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Loss of CRH → ACTH secretion decreases.