Description
Summary Abstract
Sermorelin (GHRH 1-29 NH2; hGRF 1-29; CAS 86168-78-7) is a synthetic 29-amino acid peptide corresponding to the biologically active N-terminal fragment of human growth hormone-releasing hormone (GHRH 1-44). It is the shortest synthetic fragment of GHRH retaining full biological activity at the GHRH receptor (GHRHR), a Class B G-protein-coupled receptor (GPCR) expressed on anterior pituitary somatotrophs. Sermorelin activates the Gαs/cAMP/PKA/CREB signaling cascade, driving both the synthesis and pulsatile release of endogenous growth hormone (GH) while preserving somatostatin-mediated negative feedback — a critical distinction from direct exogenous GH administration. FDA-approved under the brand name Geref® in 1997 for diagnostic evaluation of GH deficiency, sermorelin remains the canonical reference GHRH analog against which all subsequent GHRH-based secretagogues are compared.
Clinical Indications
Sermorelin’s GHRHR agonism and preserved pulsatility support investigation in the following contexts:
- Growth Hormone Deficiency Diagnosis: Sermorelin stimulation testing distinguishes hypothalamic from pituitary GH deficiency by probing pituitary somatotroph reserve; its prior FDA approval (Geref®) established validated protocols for GH axis assessment in children and adults.
- Age-Related GH Decline Research: The GH/IGF-1 axis is the first endocrine axis to decline with aging; sermorelin’s mechanism of stimulating GH mRNA transcription and increasing pituitary somatotroph reserve positions it as a research tool for GH axis restoration strategies in aging models.
- GH Secretagogue Combination Studies: The synergistic interaction between the GHRHR (sermorelin) and GHS-R1a (ghrelin mimetics: ipamorelin, GHRP-2) pathways is a well-characterized research paradigm; combination protocols produce substantially greater GH responses than either agent alone through complementary signal transduction mechanisms.
Contraindications
- Active Intracranial Neoplasm: GH stimulation is contraindicated in the presence of active pituitary or intracranial tumors, as GHRHR agonism may promote tumor growth; any protocol using sermorelin should screen for baseline pituitary pathology.
- High Somatostatin Tone States: Sermorelin’s efficacy is significantly attenuated during periods of elevated somatostatin — including postprandial states and active stress responses — due to the intact negative feedback mechanism; study timing relative to feeding and stress should be controlled.
- DPP-4-Affected Pharmacokinetics: Sermorelin is rapidly cleaved at the Ala² position by dipeptidyl peptidase-4 (DPP-4), producing inactive GHRH(3-29) with a plasma half-life of only 10–20 minutes; studies requiring sustained GHRHR engagement should employ longer-acting analogs such as CJC-1295 or tesamorelin.
Mechanism of Action (MOA)
Sermorelin functions as a selective Class B GPCR agonist on anterior pituitary somatotrophs through a well-characterized cAMP-mediated signaling cascade:
GHRHR Binding and Gαs Activation
Sermorelin binds with high affinity to the GHRHR (growth hormone-releasing hormone receptor), a Class B GPCR predominantly expressed on somatotroph cells. The N-terminal Tyr¹ residue and C-terminal amide are critical pharmacophore elements. Receptor occupancy activates the Gαs subunit, which stimulates adenylyl cyclase to elevate intracellular cAMP.
cAMP/PKA/CREB Cascade
Elevated cAMP activates protein kinase A (PKA), which phosphorylates the transcription factor CREB (cAMP response element-binding protein). Phospho-CREB binds CRE sequences in the GH1 gene promoter, driving GH gene transcription and increasing pituitary somatotroph reserve — a mechanism absent with direct GH administration.
Pulsatile GH Release and Somatostatin Feedback
The signaling cascade also triggers calcium influx through voltage-gated L-type channels, stimulating exocytosis of stored GH secretory granules. Critically, the resulting GH elevation upregulates somatostatin release from the hypothalamus, preserving the pulsatile GH secretion pattern. This self-regulating feedback loop prevents supraphysiological GH levels and distinguishes sermorelin from exogenous GH replacement.
Key Features & Specifications
Sermorelin occupies a unique position as the shortest fully functional GHRH fragment with prior FDA approval and validated clinical protocols:
Chemical Analysis
| Property | Specification Reference Data |
|---|---|
| Sequence | Tyr-Ala-Asp-Ala-Ile-Phe-Thr-Asn-Ser-Tyr-Arg-Lys-Val-Leu-Gly-Gln-Leu-Ser-Ala-Arg-Lys-Leu-Leu-Gln-Asp-Ile-Met-Ser-Arg-NH2 |
| CAS Number | 86168-78-7 |
| Molecular Formula | C149H246N44O42S |
| Molecular Weight | 3357.93 g/mol |
| Synonyms | GHRH(1-29)NH₂, hGRF 1-29, GRF 1-29, Geref® |
| Form / Variation | 5 MG Lyophilized (SKU P-037) |
Storage, Safety, and Handling
Storage Protocol
Store lyophilized sermorelin at −20 °C or below, in a sealed, desiccated container protected from light. Reconstitute with sterile bacteriostatic water for injection; once reconstituted, store at 4 °C and use within 28 days. Acetate salt form has a slightly higher mass than the free acid; account for acetate content when calculating precise molar concentrations. Avoid repeated freeze-thaw cycles.
Handling & Compliance
Handle with standard laboratory PPE. Sermorelin’s prior FDA approval status (discontinued post-market) does not exempt investigational use from institutional review requirements. The compound is subject to WADA regulations as a peptide hormone affecting the GH axis; investigators conducting studies in athletic populations should verify current WADA prohibited list status. No CYP-mediated hepatic metabolism occurs; primary inactivation is renal clearance of DPP-4-cleaved fragments.