TRH

Where it comes from

Made in

The paraventricular nucleus of the hypothalamus; also widely through the brain and spinal cord

Sent out by

Cold, and the daily rhythm; thyroid hormone feeds back to stop it

Acts on

• Pituitary thyrotrophs (TSH)
• Lactotrophs (prolactin)
• Brainstem and spinal cord (arousal, breathing)

What it does

• Releases TSH, and so thyroid hormone
• Releases prolactin from the lactotrophs, which is why a high TSH and a raised prolactin can turn up together ²
• An arousal and antidepressant signal in the brain, independent of the thyroid

In medicine

• The TRH stimulation test probed the pituitary before sensitive TSH assays; protirelin is now scarce ¹
• Taltirelin, a TRH analogue, is approved in Japan for spinocerebellar degeneration

Beyond the body’s own use

• Rovatirelin, a later analogue from the same Japanese work, improved ataxia scores modestly against placebo in two phase 3 trials ³
• TRH itself has been trialled in motor neuron disease, depression and epilepsy since the 1970s without a lasting result; a specific plasma enzyme destroys it within minutes, which is why resistant analogues were built ²
• Nothing in the family is approved outside Japan, and TRH is not used outside medicine