Thyrotrophin-releasing hormone (paraventricular nucleus)
Hypothalamus · TRH Gq Also drives prolactin
A tripeptide from parvocellular PVN neurones that acts through Gq on thyrotrophs to drive TSH synthesis and glycosylation. It is also a prolactin secretagogue.
Detail
- Stimulates
- TSH, and prolactin
- Suppressed by
- T3 generated inside the neurone from T4 by type 2 deiodinase, so the axis effectively senses T4
- Other TSH brakes
- Somatostatin, dopamine and glucocorticoids, which is why TSH is low during dopamine infusion, steroid therapy and severe illness
When it goes wrong
Long-standing untreated primary hypothyroidism
High TRH also drives prolactin: galactorrhoea and oligomenorrhoea, plus thyrotroph hyperplasia that can mimic a pituitary adenoma on MRI and resolves on thyroxine
Practise this structure
5 questions in the bank tagged Thyroid.
A 38-year-old woman presents with three weeks of aching pain in the front of her neck that worsens when she turns her head or swallows and radiates up to both e…
Clinical rotations · middle twist
A 42-year-old man was treated with radioactive iodine for Graves disease three days ago. He now reports dry mouth and painful swelling in front of both ears, wo…
Clinical rotations · common
A 34-year-old woman taking carbimazole for Graves disease presents with fever, malaise and two painful oral ulcers. She has a temperature of 38.7°C and mild cer…
Clinical rotations · common
A 35-year-old woman has palpitations and a 9 kg weight loss over 3 months. Her free thyroxine is 48 pmol/L (reference 10–22 pmol/L), TSH is less than 0.01 mIU/L…
Mechanisms of disease · common
A 38-year-old woman presents with two weeks of pain in the front of her neck radiating to her jaw, together with palpitations, sweating and 2 kg of weight loss.…
Clinical rotations · common