Hypothalamic-pituitary hormone regulation (tonic inhibition)
Framing
- The hypothalamic-pituitary axis regulates downstream endocrine glands through tonic and pulsatile hormone release, with tonic inhibition being the key regulatory principle for prolactin specifically - prolactin secretion is under constant dopaminergic inhibitory tone from the hypothalamus, meaning anything disrupting this pathway (pituitary stalk compression, dopamine-antagonist drugs) causes hyperprolactinaemia through loss of inhibition, distinct from every other anterior pituitary hormone which is predominantly under stimulatory hypothalamic control
- This inverse regulatory logic explains why a modestly elevated prolactin from stalk compression (a large non-functioning pituitary mass compressing the stalk) can be difficult to distinguish from a true prolactin-secreting microadenoma without further assessment, and why repeat confirmation of an elevated prolactin result (accounting for stress, venepuncture, and pulsatile secretion as confounders) is recommended before extensive work-up
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