Trh

TRH stands for thyrotropin-releasing hormone, a small neuropeptide produced by hypothalamic neurons. It is a tripeptide, commonly described as pyroglutamyl-histidyl-proline amide (pGlu-His-Pro-NH2). TRH is released into the hypothalamo-hypophyseal portal circulation and acts on the anterior pituitary to stimulate the secretion of thyroid-stimulating hormone (TSH) and, to a lesser extent, prolactin.

Mechanism and receptors: TRH binds to TRH receptors on pituitary thyrotrophs, which are G protein-coupled receptors. Receptor activation leads to the phospholipase C pathway, generating inositol triphosphate and diacylglycerol, increasing intracellular calcium, and promoting the synthesis and release of TSH and prolactin. The hypothalamic release of TRH is regulated by thyroid hormones (negative feedback), among other factors, and TRH signaling influences central nervous system functions beyond the pituitary.

Physiological role: The primary endocrine role of TRH is to regulate the thyroid axis via TSH release, linking hypothalamic signaling to thyroid hormone production. TRH receptors are also found in various brain regions, where TRH is believed to participate in mood, arousal, and other CNS processes. The full spectrum of central TRH actions continues to be explored in research.

Clinical relevance: The TRH stimulation test uses exogenous TRH to provoke TSH (and prolactin) release and has historically aided in evaluating pituitary function and distinguishing primary from secondary hypothyroidism. Its use has declined in routine practice due to limited availability and variable results. TRH and its analogs have been studied in research contexts for potential applications in mood disorders and neuroprotection, but are not standard therapies.