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
4 questions in the bank tagged Thyroid.
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