Thyrotropin releasing hormone (TRH or Protirelin) is a research peptide consisting of the tripeptide sequence pGlu-His-Pro-NH₂. It functions as a hypothalamic regulatory peptide that modulates pituitary secretion of thyrotropin (TSH) and prolactin through activation of the TRH receptor, a Gq-coupled GPCR. This interaction stimulates phospholipase C, IP₃, and intracellular Ca²⁺ signaling cascades involved in pituitary–thyroid axis regulation. TRH is utilized in preclinical studies of neuroendocrine feedback, receptor coupling, and second-messenger signal transduction.
