Thyrotropin-Releasing Hormone (TRH)
A 3 amino acid peptide (the smallest known hypothalamic releasing hormone) produced by the hypothalamus that stimulates TSH and prolactin release from the anterior pituitary. TRH is an example of how even very short peptides can have potent and specific biological effects.
Technical Context
TRH (pGlu-His-Pro-NH2, where pGlu is pyroglutamate) is the smallest hypothalamic releasing hormone at just 3 amino acids. It is produced in the paraventricular nucleus and acts on TRH-R1 (Gαq-coupled) on pituitary thyrotrophs to stimulate TSH release, and on lactotrophs to stimulate prolactin release. TRH demonstrates that even very short peptides can have potent and specific biological effects — a concept relevant to peptide drug design. TRH also illustrates protective modifications: the N-terminal pyroglutamate and C-terminal amidation protect this tiny peptide from aminopeptidases and carboxypeptidases respectively. The TRH stimulation test (formerly used to evaluate thyroid function) has been largely replaced by sensitive TSH assays.