Lactotroph — prolactin
Pituitary · Prolactin D2 inhibited TRH stimulated
Lactotrophs secrete prolactin continuously unless restrained by dopamine, while TRH, oestrogen and suckling push it up. Prolactin prepares and sustains the breast and suppresses GnRH.
Traced from the start
Detail
- Normal range
- Below about 500 mIU/L (25 microgram/L); it rises 10-20 fold through pregnancy as oestrogen causes lactotroph hyperplasia, enlarging the gland
- Reflex
- Suckling produces a neural surge; without suckling prolactin returns to baseline within 1-2 weeks
- Level guides the cause
- Stalk compression and drugs usually give under about 2000-3000 mIU/L (100-150 microgram/L); a macroprolactinoma typically exceeds 5000 mIU/L (250 microgram/L)
- Assay traps
- Macroprolactin (inert, IgG-bound) gives a high level in an asymptomatic patient; the hook effect gives a falsely low level with a very large tumour unless the sample is diluted
When it goes wrong
Microprolactinoma in a woman
Oligomenorrhoea or amenorrhoea, galactorrhoea and infertility; cabergoline is first line and shrinks macroadenomas too, so surgery is second line even for large tumours
Any large sellar mass compressing the stalk
Modest hyperprolactinaemia with deficiency of the other axes — the pattern that separates the stalk effect from a true prolactinoma, where the level tracks tumour size
Practise this structure
2 questions in the bank tagged Pituitary.
A 52-year-old woman has progressive headaches and difficulty seeing objects to either side. MRI shows a 2.6-cm sellar mass elevating and compressing the optic c…
Clinical rotations · middle twist
A 44-year-old man has an incidental 8-mm pituitary lesion discovered during MRI for headaches. He has normal visual fields, normal pituitary hormone testing, an…
Clinical rotations · middle twist