Protirelin (TRH)

Prescription

Protirelin is synthetic thyrotropin-releasing hormone (TRH), a remarkably tiny peptide — just three amino acids (pyroglutamyl-histidyl-proline amide). Despite its small size, TRH sits near the top of the thyroid axis: released by the hypothalamus, it stimulates the pituitary to secrete thyroid-stimulating hormone (TSH) and also prolactin. Because the response is fast and measurable, protirelin has long been used as a diagnostic probe of pituitary function. In the classic TRH stimulation test, a baseline TSH is drawn, protirelin is injected, and TSH (and sometimes prolactin) is measured over the following 30–60 minutes. The pattern of the TSH response helps characterize thyroid and pituitary disorders. An exaggerated response can suggest primary hypothyroidism or point to certain pituitary problems, while a flat (absent) response is seen in hyperthyroidism and some pituitary conditions. Historically the test was widely used to diagnose subtle thyroid dysfunction, but the advent of sensitive third-generation TSH assays — which can measure very low TSH directly — has reduced its everyday need in many countries. It retains niche diagnostic value, for example in evaluating central hypothyroidism, some pituitary tumors, and in research on the thyroid and prolactin axes. Mechanistically, protirelin binds TRH receptors on pituitary thyrotroph and lactotroph cells, triggering release of stored TSH and prolactin. Administration commonly causes brief, harmless sensations — a transient urge to urinate, a metallic taste, flushing, or a short rise in blood pressure — that pass within minutes. Protirelin was formerly available in the United States (as Thyrel TRH) but has been discontinued there; it continues to be used in some European and Asian countries. This page is an educational reference on the peptide and its diagnostic role; any testing is arranged and interpreted by an endocrinologist.