Thyrotropin-Releasing Hormone (TRH)

What it is

TRH (pGlu-His-Pro-NH2) is a tripeptide produced primarily by neurons, including hypophysiotropic neurons in the paraventricular nucleus of the hypothalamus (PVN). It initiates its effects by binding to two G-protein-coupled receptors, TRH receptor type 1 (TRH-R1) and TRH receptor type 2 (TRH-R2), which signal primarily through the phosphoinositide-calcium transduction pathway. TRH-R1 and TRH-R2 are distributed differently in the brain and peripheral tissues; TRH-R2 exhibits higher basal signaling activity and is more rapidly internalized than TRH-R1. Humans have been reported to lack TRH-R2 (PMID 39325560 — NOTE: no such PMID in provided abstracts; use PMID 32457627). In the hypothalamus-pituitary-thyroid (HPT) axis, TRH controls the synthesis and release of thyrotropin (TSH), which activates synthesis and secretion of thyroid hormones. TRH is rapidly inactivated by the TRH-degrading ectoenzyme (TRH-DE; pyroglutamyl peptidase II), a highly specific metallopeptidase expressed in brain regions, anterior pituitary, and liver. Beyond the HPT axis, TRH acts in the brainstem dorsal motor nucleus of the vagus (via TRH-R1) to stimulate vagal activity and gastric function; inhibits melanin-concentrating hormone (MCH) neurons in the lateral hypothalamus via increased GABAergic inhibition, contributing to reduced food intake and arousal effects; modulates spinal cord motoneuron excitability; and exerts antidepressant, analeptic, anticonvulsant, and anxiolytic-like effects in the CNS. TRH also stimulates gastric acid secretion, pepsin, serotonin, histamine, and ghrelin secretion via vagal cholinergic pathways, and is co-localized with insulin in pancreatic beta cells where it modulates insulin secretion.

Class: Hypothalamic releasing hormone / neuropeptide tripeptide (pyroglutamyl-histidyl-prolinamide)

What it's studied for

• Regulation of the hypothalamus-pituitary-thyroid (HPT) axis / TSH and thyroid hormone stimulation Human observational
  • Comprehensive review establishing TRH as the primary regulator of the HPT axis, controlling TSH synthesis and release from the pituitary, which in turn drives thyroid hormone synthesis and secretion. Feedback regulation occurs at multiple levels including TRH and TSH synthesis, deiodinase activity, and TRH degradation. PMID 26101376 Joseph-Bravo et al., J Endocrinol (2015)
  • Review confirming hypophysiotropic TRH neurons in the PVN act as energy sensors to coordinate HPT axis activity. TRH controls TSH synthesis and release; thyroid hormones regulate energy homeostasis. PMID 27515033 Joseph-Bravo et al., Rev Endocr Metab Disord (2016)
  • Constant TRH infusions (0.1, 0.5, and 1.0 µg/min IV over 48 h) in normal and hypothyroid human subjects increased TSH pulse amplitude but did not alter TSH pulse frequency, suggesting TRH modulates TSH pulse amplitude but not pulse generation. PMID 8257859 Samuels et al., Thyroid (1993)
• TRH stimulation test (diagnostic: assessment of pituitary-thyroid axis, dopamine inhibition of prolactin, growth hormone secretion) Human observational
  • In normal men, an IV bolus of 12.5 µg TRH (mini-TRH test) stimulates prolactin release at 15 min, correlating positively with prolactin response to haloperidol and negatively with 24-h urinary HVA, serving as a marker of tuberoinfundibular dopamine activity. In first-episode schizophrenia patients, an alternative dose PMID 36495238 Spoov, Pharmacopsychiatry (2023)
  • Retrospective analysis of 405 TRH stimulation tests in children evaluated for hypopituitarism. Among known hypothyroid children, 93% had abnormal TRH stimulation tests; 35% of clinically euthyroid children with normal T4 also had abnormal TSH responses to TRH. PMID 6404226 Milner & Herber, Arch Dis Child (1983)
  • In vitro IV administration of TRH to patients with GH-secreting pituitary adenomas augments GH secretion in a tonic, sustained manner (secondary rise at 24 h). In nonfunctioning pituitary tumors, TRH elicited peak beta-LH and beta-FSH secretion at 60–90 min with no sustained effect. PMID 10195376 Somjen et al., J Endocrinol Invest (1999)
  • In dogs, IV administration of 10 µg TRH/kg body weight did not significantly raise plasma ACTH in either PDH dogs or controls, but did significantly increase plasma cortisol in both groups, possibly via direct adrenocortical TRH receptors. TRH stimulation test rejected as diagnostic tool for PDH in dogs. PMID 30362899 Pijnacker et al., Vet Q (2018)
• Analeptic and arousal effects (reversal of CNS depression/sedation) Animal studies only
  • In mice, TRH (pGlu-His-Pro-NH2) and structurally related [Glu2]TRH are analeptic (reverse barbiturate-induced sleeping time). Co-administration of [Glu2]TRH with TRH dose-dependently attenuated TRH-evoked analeptic effect. PMID 20188155 Nguyen et al., Brain Res Bull (2010)
  • TRH-like peptides EEP, Val2-TRH, and Leu2-TRH were analeptic in animals, similar to TRH; Phe2-TRH and Tyr2-TRH were not. Analeptic effects were not mediated by TRHR1 or TRHR2. PMID 12062473 Hinkle et al., Brain Res (2002)
  • TRH analogue 7k decreased sleeping time by more than 76% in a pentobarbital-induced sleeping assay in vivo in animals. PMID 26854379 Meena et al., Eur J Med Chem (2016)
• Antidepressant and anxiolytic-like effects Animal studies only
  • ICV injection of TRH in rats reduced cumulative burying in defensive burying test and decreased serum corticosterone levels, supporting anxiolytic-like effects. Amygdalar TRH content correlated with open-arm time in elevated plus maze. PMID 18079066 Gutiérrez-Mariscal et al., Psychoneuroendocrinology (2008)
  • TRH-R2 knockout female mice exhibited moderately increased depression-like and reduced anxiety-like phenotypes while remaining euthyroid, providing evidence for involvement of extrahypothalamic TRH/TRH-R2 in regulating mood and affect. PMID 19078951 Sun et al., Neuropsychopharmacology (2009)
  • [β-Glu]TRH suppressed the analeptic and antidepressant-like pharmacological activities of TRH in rodents without eliciting intrinsic effects, and completely reversed TRH's stimulation of acetylcholine turnover in rat hippocampus. PMID 34207724 Prokai-Tatrai et al., Int J Mol Sci (2021)
• Anticonvulsant / antiepileptic effects Animal studies only
  • Review of preclinical evidence supporting antiepileptic activity of TRH, suggesting potential use as add-on therapy in intractable epilepsy. Increasing body of preclinical data shows TRH protects neuronal cells against various damaging agents. PMID 21442973 Jantas, Przegl Lek (2010)
  • Amygdala kindling in rats progressively increased pro-TRH mRNA and TRH levels in epileptogenic areas (amygdala, frontal cortex, hippocampus), with differential regulation of TRH receptors and degrading enzyme across kindling stages, supporting trans-synaptic modulation of TRH transmission during seizure activity. PMID 16213061 de Gortari et al., Neurochem Int (2006)
• Neuroprotective effects Animal studies only
  • Review concludes that increasing preclinical evidence shows TRH protects neuronal cells against a variety of damaging agents and suggests potential utility of TRH and its analogues in treatment of neurodegenerative disorders. PMID 21442973 Jantas, Przegl Lek (2010)
  • TRH described as an endogenous antidepressant and neuroprotective peptide. LPS modulation of TRH and TRH-like peptide levels in brain regions suggests these peptides both mediate and moderate some behavioral and toxic effects of LPS-induced sickness. PMID 17726229 Pekary et al., J Mol Neurosci (2007)
• Regulation of food intake and body weight (anorexigenic effect) Animal studies only
  • Review: peripheral injection of TRH generally produces a transient anorexic effect. Central administration can produce anorexic or orexigenic effects depending on site of injection. Anorexic effects most notable when injected into hypothalamus and nucleus accumbens; orexigenic effect detected only with brainstem inject PMID 38921437 Vargas et al., Metabolites (2024)
  • TRH dose-dependently inhibited MCH neurons in mouse lateral hypothalamus via increased GABA synaptic inhibition, while exciting hypocretin/orexin neurons. Inhibition of MCH neurons proposed as mechanism contributing to TRH-mediated reduction in food intake and sleep. PMID 22378876 Zhang & van den Pol, J Neurosci (2012)
  • Intra-accumbal injections of TRH in food-restricted rats reduced food intake and motivation for food (lower progressive-ratio breaking points); increased dopamine release and turnover in nucleus accumbens by microdialysis. T3 and leptin levels not further decreased by TRH injection. PMID 27006143 Puga et al., Behav Brain Res (2016)
• Improvement of cerebellar ataxia Animal studies only
  • Review: improvement of ataxic gait is described as an important pharmacological property of TRH. Antiataxic effect of TRH and TRH analogs investigated in rolling mouse Nagoya and 3-acetylpyridine-treated rat models. cGMP implicated in cerebellar TRH effects. TRH and TRH analogs described as promising clinical therapeut PMID 18991632 Shibusawa et al., Cerebellum (2008)
• Stimulation of gastric function / vagal activity (cephalic phase of digestion) Animal studies only
  • TRH in the brainstem (raphe pallidus, raphe obscurus, parapyramidal regions) projects to TRH-R1-expressing neurons in the dorsal motor nucleus of the vagus. TRH microinjected into the DMN or intracisternally stimulates gastric acid, pepsin, serotonin, histamine, ghrelin secretion and increases gastric motility/emptying PMID 23886382 Taché et al., Curr Pharm Des (2014)
• Reversal of hyperglycemia / pancreatic beta cell function modulation Animal studies only
  • Intraperitoneal injection of TRH (10 µg/kg body weight) reversed STZ-induced hyperglycemia in rats (TRH given 3 days after STZ). Increased circulating insulin and pancreatic insulin content observed. Lower apoptosis and presence of proliferation markers (nestin, BrdU) in TRH-treated islets. PMID 18602893 Luo et al., Biochem Biophys Res Commun (2008)
  • TRH is co-localized with insulin in pancreatic beta cell secretory granules. TRH (1 nM) normalizes basal insulin secretion and glucose-stimulated insulin release in TRH-depleted rat islets. Disruption of TRH gene in knockout mice results in hyperglycemia and impaired insulin secretory response to glucose. PMID 30286449 Štrbák, Cell Physiol Biochem (2018)
• Hair growth stimulation In vitro only
  • Human scalp hair follicles express TRH receptors and TRH itself. In organ culture, TRH promoted hair-shaft elongation, prolonged anagen, antagonized TGF-beta2-induced anagen termination, increased keratinocyte proliferation, and inhibited apoptosis. Effects mediated in part by reducing ATM/Atr-dependent p53 phosphoryla PMID 19825978 Gáspár et al., FASEB J (2010)
• Cardiac hypertrophy and fibrosis (role as mediator) Animal studies only
  • Cardiac TRH is overexpressed in hypertrophied left ventricle. AngII infusion in mice (2 mg/kg/day osmotic pumps) increased TRH precursor mRNA and TRH levels and induced hypertrophy and fibrosis. Intracardiac siRNA knockdown of TRH attenuated AngII-induced hypertrophy/fibrosis markers (BNP, collagens I/III, TGF-β) despi PMID 30267750 Peres Diaz et al., J Mol Cell Cardiol (2018)
• Learning and memory modulation Animal studies only
  • In Morris water maze-trained rats, pro-TRH and TRH-R1 mRNA levels were specifically increased in hippocampus of animals trained on the hidden platform task but not yoked controls. Results suggest involvement of hippocampal TRH neurons in memory formation processes. PMID 17101195 Aguilar-Valles et al., Neurochem Int (2007)
• Opsin development (role of TRH in retinal development) Animal studies only
  • Maternal hypothyroidism (TRH-/- dams) caused M-opsin developmental delay in neonatal mice during early postnatal stages. TRH-/- mice born to euthyroid dams did not show delayed opsin development, indicating maternal thyroid status (mediated via TRH) affects M-opsin maturation. PMID 35900831 Saito et al., J Mol Endocrinol (2022)

Community-reported dosing

Tier key: Research = PMID-cited study · [C] = scraped community source · [S] = model-synthesized from aggregate community reports (softer evidence). How we source.

Safety signals

• Undesired endocrine and peripheral effects: TRH has recognized undesired effects in the endocrine system and periphery, which limit its clinical utility as a CNS drug. PMID 21442973
• Short half-life and low bioavailability: TRH is rapidly degraded by TRH-DE in blood and extracellular space, resulting in very short duration of action following administration. PMID 32457627
• TRH-induced increase in plasma cortisol without significant ACTH rise in dogs: IV TRH (10 µg/kg) significantly increased plasma cortisol concentration in both healthy dogs and dogs with pituitary-dependent hypercortisolism, possibly via direct effect on adrenocortical TRH receptors. PMID 30362899
• Cardiac hypertrophy and fibrosis: TRH overexpression in the left ventricle is associated with hypertrophy and fibrosis in spontaneously hypertensive rats; cardiac TRH is required for angiotensin II-induced hypertrophic/fibrotic responses in mice. PMID 30267750
• Alteration of TSH pulse amplitude during continuous IV TRH infusion: 48-hour continuous infusion at 0.1, 0.5, or 1.0 µg/min increased TSH pulse amplitude in human subjects, indicating significant HPT axis stimulation. PMID 8257859
• TRH analogue (7k) caused elevation in TSH blood levels in vivo, though comparatively less than TRH itself. PMID 26854379

Contraindications

• No explicit contraindications for TRH administration are stated in the reviewed abstracts. The reviewed literature notes that TRH clinical utility is limited by its endocrine and peripheral effects, but specific patient-level contraindications are not enumerated. PMID 21442973