Endocrine regulation · USMLE Step 1

Which regulatory mechanism is least likely to apply to the secretion of prolactin from the anterior pituitary under physiological conditions?

  1. Inhibitory regulation by dopamine from the hypothalamus
  2. Stimulation by thyrotropin-releasing hormone (TRH)
  3. Positive feedback from elevated prolactin levels
  4. Suppression by high estrogen levels
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Correct answer: Positive feedback from elevated prolactin levels

Prolactin release is primarily under inhibitory control by hypothalamic dopamine, with additional modulation by TRH and estrogen; it is not classically regulated by positive feedback from its own levels.

Difficulty: Medium Question 14 of 23

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