What Is Sermorelin?
Sermorelin (GHRH 1-29 NH₂) is a 29-residue peptide corresponding to the first 29 amino acids of the 44-residue hypothalamic growth hormone-releasing hormone (GHRH). It was identified in the early 1980s as the minimal fragment of GHRH retaining full GHRH receptor (GHRH-R) binding affinity and GH secretagogue activity.
The full-length GHRH (1-44) is produced in the hypothalamic arcuate nucleus and travels via the hypophyseal portal blood to the anterior pituitary, where it binds GHRH-R on somatotrophs to stimulate GH synthesis and release. Sermorelin recapitulates this signalling with a short, defined half-life — making it the gold-standard tool peptide for studies requiring discrete GH pulse induction.
GHRH Receptor Mechanism
The GHRH receptor is a class B G-protein coupled receptor (GPCR) coupled to Gs. Sermorelin binding activates adenylyl cyclase, raising intracellular cAMP levels in pituitary somatotrophs. This activates PKA, which phosphorylates multiple targets involved in:
- GH gene transcription: PKA phosphorylates CREB (cAMP response element-binding protein), driving GH gene expression
- GH exocytosis: PKA activates voltage-gated Ca²⁺ channels and mobilises GH secretory granules
- Somatotroph proliferation: Chronic GHRH-R activation drives pituitary somatotroph cell proliferation (relevant in acromegaly models)
Gs-coupled → adenylyl cyclase → ↑cAMP → PKA activation
PKA → CREB phosphorylation → GH gene transcription → ↑GH protein
PKA → VGCC activation → Ca²⁺ influx → GH granule fusion
Somatostatin opposes GHRH-R via Gi/cAMP reduction — net GH output = GHRH − SRIF tone
Sermorelin's short half-life (DPP-IV cleaves at position 2 Ala) means it produces brief, pulse-like GH release rather than sustained elevation — closely mimicking the physiological hypothalamic GHRH pulse that occurs every 90–120 minutes.
GH Pulse Profile
The pharmacokinetic profile of Sermorelin produces a characteristic GH response in animal models:
Sermorelin GH Response (Rodent SC, 1–10 µg/kg)
| Parameter | Value |
|---|---|
| Peak GH onset | 15–30 min post-injection |
| Peak GH level | 3–6× baseline (dose-dependent) |
| Return to baseline | 90–120 min |
| IGF-1 rise (chronic 14d) | +25–45% above control |
| Receptor desensitisation | Minimal with pulsatile (2–3×/day) dosing |
The pulsatile GH pattern is considered physiologically superior to continuous GH elevation for many downstream effects, including maintaining GH receptor sensitivity, preserving normal GH feedback loops, and avoiding the metabolic disturbances (insulin resistance, fluid retention) associated with supraphysiological constant GH exposure.
Clinical Research History
Sermorelin was the only GHRH analogue to receive FDA approval (as Geref, Serono), used clinically as a diagnostic test for GH deficiency and as a therapeutic agent in paediatric GH deficiency where pituitary function is intact (hypothalamic GHD). It was withdrawn from the US market in 2008 for commercial reasons (not safety concerns), as recombinant GH dominated the market.
Key Clinical Findings
- GH deficiency diagnosis: IV Sermorelin (1 µg/kg) produces a GH peak ≥10 µg/L in normal subjects; subnormal response indicates GH deficiency or pituitary dysfunction
- Paediatric GHD treatment: SC Sermorelin twice daily increased linear growth velocity in GH-deficient children, though less effectively than recombinant GH in head-to-head comparisons
- Adult GHD: Phase II data showed improvements in body composition, bone mineral density, and quality-of-life scores in GH-deficient adults after 6 months of treatment
- Age-related GH decline: Research in healthy older adults demonstrated Sermorelin raised IGF-1 to mid-normal range for age with improved sleep architecture (increased slow-wave sleep) — consistent with GH's sleep-modulatory role
Sermorelin vs CJC-1295 vs Native GHRH
| Property | GHRH 1-44 (native) | Sermorelin (1-29) | CJC-1295 (no-DAC) | CJC-1295-DAC |
|---|---|---|---|---|
| Length | 44 AA | 29 AA | 30 AA (modified) | 30 AA + DAC |
| Half-life | ~7 min (plasma) | 10–20 min | ~30 min | 6–8 days |
| GH profile | Pulse | Pulse | Pulse | Sustained "bleed" |
| DPP-IV stability | Low | Low | High (Ala→Aib substitution) | High |
| Research use | Short-term mechanistic | ✓ Pulsatile GH research | ✓ Enhanced pulsatile | Extended GH elevation |
Sermorelin occupies a unique niche: it is the closest to native GHRH physiology while offering practical synthesis and formulation advantages over the full 44-AA sequence. For research designs requiring physiologically-timed GH pulses without extended biological half-life, Sermorelin remains the reference GHRH tool peptide.
Research Protocols
GH Secretion Studies
- Dose: 1–10 µg/kg SC or IV (rodent)
- Timing: At the onset of the active phase (lowest somatostatin tone)
- Measurement: Serial blood sampling q15 min × 2 h (GH ELISA)
- Controls: Saline, GHRH antagonist (GHRH-Ant), hypophysectomised controls
IGF-1 Axis (Chronic)
- Dose: 1–5 µg/kg SC BID–TID × 14–28 days
- Endpoints: Serum IGF-1 (terminal bleed), body weight, liver GH receptor mRNA
- Pair with: DXA (body composition) if available
Sleep Architecture Research
- Model: EEG-implanted rats or non-human primates
- Dose: Pulsatile infusion or bolus pre-sleep onset
- Endpoint: Slow-wave sleep (SWS) duration, GH pulse correlation
- Reference: GH release is maximal during SWS (circadian link)
Safety Profile & Stability Notes
- Immunogenicity: Low in clinical experience; anti-Sermorelin antibodies occasionally detected but without clinically meaningful attenuation of GH response in most subjects
- Injection site reactions: Mild transient reactions at SC injection sites reported in clinical paediatric use; considered minor adverse events
- Hypersensitivity: Rare; standard precautions apply in animal models
- Stability: Lyophilised Sermorelin is stable at −20°C for 24 months; reconstituted in bacteriostatic water (0.9% benzyl alcohol) stable 7–14 days at 4°C
- DPP-IV sensitivity: Rapid plasma degradation limits systemic distribution; this is a feature in physiological studies (clean pulse) but means repeated dosing is required for chronic protocols
FAQ
What is Sermorelin?
Sermorelin is a synthetic 29-amino-acid peptide corresponding to the first 29 residues of endogenous GHRH. It activates the pituitary GHRH receptor to stimulate GH release in a pulsatile, physiological pattern.
How does Sermorelin differ from CJC-1295?
Sermorelin has a short half-life (10–20 min) producing brief GH pulses. CJC-1295-DAC extends half-life to 6–8 days via albumin binding, producing sustained GH elevation. For pulsatile GH research, Sermorelin is preferred; for sustained GH elevation studies, CJC-1295-DAC is used.
Was Sermorelin ever FDA-approved?
Yes — as Geref (Serono) for paediatric GH deficiency diagnosis and treatment in children with intact pituitary function. It was withdrawn from the US market in 2008 for commercial reasons, not safety concerns.
Does Sermorelin work if the pituitary is damaged?
No — Sermorelin requires intact pituitary somatotrophs and functional GHRH-R. It cannot stimulate GH release in primary pituitary failure. It works specifically for hypothalamic GH deficiency where the pituitary itself is responsive but lacks adequate GHRH input.
Sermorelin for Research
Lyophilised Sermorelin ≥98% purity (HPLC) with full COA and mass spec verification available from Rainbow Peptide.
View Sermorelin →