Somatropin (HGH)

Somatropin is a 191-amino-acid recombinant human growth hormone (rhGH) used in South African laboratories for in-vitro and preclinical IGF-1 signalling work. As of 2026, it is available locally in two practical research formats: the Body Pharm 40 IU pen and the 100 IU multi-vial kit. This guide covers 2026 ZAR pricing, how somatropin works at the molecular level, a pen-versus-kit format comparison, and SAHPRA's regulatory position on rhGH for research use.

You will find here how somatropin activates the GH receptor and drives IGF-1 production, which format suits your experimental design, and what regulatory approvals you need before ordering in South Africa.

A frank caveat upfront: finished HGH products may be lawfully imported into some jurisdictions only when intended solely for in-vitro or animal laboratory research under recognised research-import provisions. South African researchers should treat somatropin sourcing as a regulated workflow, not a retail transaction.

Key Takeaways

• Somatropin is recombinant 191-amino-acid rhGH that activates the GH receptor directly, bypassing pituitary feedback and producing clean dose-response curves for research.
• The 40 IU pen suits single-operator fixed-dose work; the 100 IU kit suits multi-assay labs running parallel dilutions at custom concentrations.
• Both formats reconstitute with bacteriostatic water and remain stable for 28 days at 2–8 °C. Freeze-thaw cycles degrade the molecule and must be avoided.
• Somatropin is Schedule 4 in South Africa and requires institutional ethics approval and SAHPRA import authorisation for research use.
• Choose somatropin for direct GHR kinetics and dose-response work; use secretagogues like CJC-1295 when the research question concerns endogenous pulsatile dynamics.

What Is Somatropin (Recombinant HGH)?

Somatropin is a 191-amino-acid recombinant analogue of endogenous human growth hormone, produced via recombinant DNA technology and used in laboratories as the reference rhGH compound for GH-axis signalling research. Its primary sequence is identical to pituitary-derived hGH, with a molecular mass of approximately 22,124 Da (approximately 22 kDa) and two intramolecular disulphide bridges stabilising the four-helix bundle fold.

Expression systems matter for downstream characterisation. Somatropin is most commonly expressed in Escherichia coli, yielding non-glycosylated 191-aa protein matching native hGH, or in mammalian cell lines for batches requiring eukaryotic post-translational handling. Somatrem, the obsolete 192-aa N-methionyl variant from earlier E. coli constructs, should not be confused with current somatropin material. The first recombinant hGH product entered international clinical use in 1985 (historical reference).

One distinction worth being clear on before ordering material: somatropin is the GH molecule itself. It acts directly at the hepatic and peripheral GH receptor to drive JAK2/STAT5 (Janus kinase 2/Signal Transducer and Activator of Transcription 5) transcription of IGF-1. It is not a secretagogue. Compounds such as CJC-1295 (a GHRH analogue) and ipamorelin (a ghrelin-receptor agonist) act upstream on the somatotroph to stimulate endogenous GH release, producing pulsatile rather than bolus exposure. Direct rhGH administration in models bypasses pituitary feedback entirely, which is why it remains the gold-standard positive control when quantifying IGF-1 LR3 downstream readouts or comparing receptor-level versus hypothalamic-pituitary interventions.

IGF-1 Signalling: Why Researchers Use Somatropin

Somatropin acts directly at the GH receptor and produces a dose-controlled IGF-1 readout. Upstream secretagogues depend on intact pituitary function and pulsatile release. For in-vitro work and tightly designed preclinical models, that mechanistic directness is the entire reason rhGH remains the reference compound.

The cascade is well-characterised. Somatropin binds two GH receptor (GHR) monomers, triggering a conformational rearrangement of the pre-formed receptor dimer. This activates receptor-associated JAK2 kinases, which trans-phosphorylate each other and then phosphorylate STAT5 (predominantly STAT5b in hepatocytes). Phosphorylated STAT5 dimerises, translocates to the nucleus, and drives transcription of IGF1, IGFBP3, and ALS. The hepatic IGF-1 output is the principal endocrine effector, and it is the variable most researchers actually quantify.

Direct receptor agonism vs upstream secretagogues

CJC-1295 (GHRH analogue), ipamorelin (ghrelin/GHS-R1a agonist), and tesamorelin all act on the somatotroph to evoke endogenous GH pulses. This approach is useful for physiological modelling because it preserves the pituitary's natural feedback loops. The resulting GH exposure is, however, pulsatile and variable between animals. Somatostatin tone and pituitary reserve confound the readout. Direct rhGH bypasses all of that. For receptor-occupancy curves, STAT5 phosphorylation timecourses, or hepatocyte IGF-1 induction assays, somatropin gives a clean dose-response that secretagogues cannot match.

IGF-1 as the downstream readout

In rodent models, serum IGF-1 typically peaks several hours after a single rhGH bolus and remains elevated through the 9–20 hour window. This reflects the lag between STAT5 activation and hepatic protein output. Researchers comparing receptor-level kinetics often pair somatropin arms with an IGF-1 LR3 arm, since LR3's reduced IGFBP affinity gives a longer free-IGF-1 exposure and isolates IGF-1R signalling from upstream GH-axis variability. The two compounds answer different questions: somatropin tests the full GH→IGF-1 cascade; LR3 tests IGF-1R-only effects.

That separation matters when interpreting endpoints. Lean-mass, glucose handling, and lipolysis readouts under somatropin reflect both direct GHR effects (adipose, muscle) and indirect IGF-1-mediated effects, whereas LR3 isolates the latter.

Body Pharm Somatropin: Pen vs Kit, Which Format Suits Your Research?

The pen suits single-operator, fixed-dose bench work. The kit suits multi-assay labs running parallel dilutions. Both are recombinant 191-amino-acid somatropin supplied lyophilised for research use only, and both reconstitute with bacteriostatic water (0.9% benzyl alcohol) or sterile water when same-day use is planned. The choice is logistical, not pharmacological: the active molecule is identical.

Side-by-side comparison

Attribute	40 IU pen	100 IU kit
Total content	40 IU (approximately 13.3 mg equivalent)	100 IU (approximately 33.3 mg equivalent), multi-vial
Format	Pre-loaded cartridge pen	Lyophilised vials + diluent ampoules
Reconstitution	Fixed cartridge volume, pre-set dose dialling	Custom: typical 1 ml bacteriostatic water per 10 IU vial gives 10 IU/ml
Dose precision	Pen-dialled increments (convenient, less flexible)	Operator-controlled, any concentration
Lyophilised storage	2–8 °C	2–8 °C
Post-reconstitution	2–8 °C, use within 28 days	2–8 °C, use within 28 days
Best fit	Single researcher, repeat fixed dosing	Multi-arm studies, varied concentrations
ZAR price (May 2026)

Reconstitution and concentration guidance

For the kit, 1 ml of bacteriostatic water per 10 IU vial yields 10 IU/ml (approximately 3.3 mg/ml). This is the concentration most rodent IGF-1 induction protocols assume. Halving the diluent to 0.5 ml doubles concentration to 20 IU/ml when injection volume is constrained. The pen's cartridge concentration is fixed by the manufacturer. Verify the printed IU/ml on the cartridge label before dose calculations, as Body Pharm pen specifications are not independently verifiable from public 2026 documentation.

Sterile water is acceptable when the reconstituted solution will be aliquoted and used within 24 hours. Bacteriostatic water is the practical default for the 28-day cold-chain window because it contains a preservative. Freeze-thaw cycles degrade somatropin's tertiary structure and reduce STAT5 activation efficacy, so aliquot before the first freeze if long-term storage is required.

Choosing for the experimental design

If your protocol uses CJC-1295 as a secretagogue comparator and somatropin as the direct-agonist arm at a single fixed dose, the pen reduces dosing variance between cages. If you are titrating across a dose-response curve or pairing somatropin with IGF-1 LR3 at multiple concentrations, the kit's custom dilution is more economical per assay. Neither format is registered with SAHPRA for human therapeutic use, and both must be handled under research-use-only conditions.

Reconstitution Protocol for the 40 IU Pen

Reconstitute the 40 IU cartridge with 1 ml of bacteriostatic water for a working concentration of 40 IU/ml (approximately 13.3 mg/ml equivalent), assuming standard Body Pharm batch labelling. Confirm the printed IU on your specific cartridge before calculating, as exact fill can vary by batch.

The procedure below is for in-vitro and preclinical research handling only.

1. Lay out 1 ml bacteriostatic water (0.9% benzyl alcohol), a 1 ml insulin syringe (29–31 G), two alcohol swabs, and the pen cartridge equilibrated to room temperature.
2. Swab the rubber septum of both the diluent vial and the cartridge for 10 seconds each.
3. Draw 1 ml bacteriostatic water and inject it slowly down the inner glass wall of the cartridge. Direct injection onto the lyophilised cake shears the 191-amino-acid chain and reduces receptor-binding potency.
4. Swirl the cartridge gently between your palms for 20–30 seconds until the solution is clear. Do not vortex, invert sharply, or shake.
5. Calculate working concentration: 40 IU ÷ 1 ml = 40 IU/ml. For a 4 IU experimental aliquot, draw 0.1 ml.
6. Store at 2–8 °C and discard at 28 days. Aliquot before any freeze step to protect tertiary structure and preserve downstream IGF-1 LR3 induction in dose-response work.

2026 Pricing in South Africa (ZAR)

Current ZAR pricing for the Body Pharm Somatropin range is shown on the product page at order time. The two formats compare as follows.

Format	Notes
Body Pharm Somatropin 40 IU pen	Single cartridge, prefilled device
Body Pharm Somatropin 100 IU kit	10 × 10 IU vials, bacteriostatic water typically sold separately

The 100 IU kit generally yields a lower cost-per-IU than the pen because the pen carries device-tooling overhead, the trade-off discussed in the format comparison above. Domestic courier shipping within South Africa is typically quoted separately and depends on whether cold-pack handling is requested. Confirm transit specifications with JCSG.org before dispatch.

Researchers comparing direct rhGH spend against upstream secretagogue protocols should price CJC-1295 and downstream IGF-1 LR3 for a like-for-like cost-per-experiment calculation. Page last verified: 12 May 2026.

SAHPRA Regulatory Status in South Africa (2026)

Somatropin is a Schedule 4 substance under the Medicines and Related Substances Act 101 of 1965 (as amended) in South Africa. Therapeutic supply requires a valid prescription from a medical practitioner registered with the Health Professions Council of South Africa. SAHPRA (the South African Health Products Regulatory Authority) administers scheduling, registration, and import authorisation for all recombinant biologics, including rhGH.

For clinical use, dispensing must occur through a licensed pharmacy against a Schedule 4 script. There is no over-the-counter pathway, and personal importation for self-administration is not a recognised route.

Research-Use Supply

Research-grade recombinant somatropin intended for in-vitro assays or preclinical animal work sits outside the prescription channel but is not unregulated. Institutional researchers should expect three compliance checkpoints before procurement:

• Approval from the institution's Institutional Ethics Committee (IEC) or Animal Research Ethics Committee (AREC), with a clearly scoped protocol identifying the rhGH application.
• A SAHPRA import permit where the material is sourced from outside South Africa, or confirmation that the domestic supplier holds the appropriate authorisation.
• Documented chain-of-custody and storage controls aligned with the institution's biosafety standard operating procedures (SOPs).

Your IEC secretariat is the correct first call. They will confirm whether your protocol triggers a Section 21 application, a standard import permit, or a domestic-supplier exemption based on current SAHPRA correspondence.

Supplier Position and Buyer Responsibility

JCSG.org lists Body Pharm Somatropin for research use only. The end user carries responsibility for ensuring the intended application complies with SAHPRA scheduling, institutional ethics approval, and any provincial requirements that apply to biologic handling. Nothing on this page constitutes legal or regulatory advice. Verify your specific protocol with your IEC and, where needed, directly with SAHPRA before placing an order.

Upstream secretagogues such as CJC-1295 and downstream effectors like IGF-1 LR3 carry their own scheduling considerations that differ from somatropin's Schedule 4 status and warrant separate verification.

Somatropin vs GH Secretagogues: Choosing the Right Research Tool

Use somatropin when your protocol requires direct, dose-controlled GHR activation without hypothalamic or pituitary variability. Use a secretagogue when the research question concerns endogenous pulse dynamics. The choice is methodological, not preferential, and it determines which confounders your model will carry.

Direct rhGH administration delivers a known molar quantity to the receptor. This is what you want for dose-response curves, GHR binding kinetics, or in-vitro hepatocyte IGF-1 induction assays. Secretagogues introduce an upstream layer of biological noise, useful when that noise is the variable under study. CJC-1295 and ipamorelin are appropriate when modelling somatotroph responsiveness, GHRH-receptor desensitisation, or the amplitude and frequency of GH pulses in conscious rodents. Tesamorelin narrows the question further, with most published models targeting visceral adipose tissue endpoints rather than systemic anabolism. IGF-1 LR3 bypasses the GH axis entirely and is the correct tool when you need to isolate downstream PI3K/Akt or MAPK (mitogen-activated protein kinase) signalling from any GHR-level interference.

Quick Decision Matrix

Research question	Preferred tool	Why
GHR dose-response, direct receptor kinetics	Somatropin	No upstream variability
Endogenous GH pulse architecture	CJC-1295 + ipamorelin	Preserves pituitary feedback
Visceral adipose-specific endpoints	Tesamorelin	GHRH analogue with targeted literature
Downstream IGF-1R signalling in isolation	IGF-1 LR3	Bypasses GHR entirely
Hepatic IGF-1 induction assays	Somatropin	Quantifiable input dose

A practical note from protocol review: mixing somatropin with a secretagogue in the same cohort without a clear factorial design usually produces uninterpretable IGF-1 data. Pick the tool that matches the question, and reserve combination arms for studies explicitly powered to detect interaction effects.

Storage, Stability, and Cold-Chain Handling

Lyophilised somatropin should be held at 2–8 °C and remains stable for up to 24 months from manufacture when kept sealed, desiccated, and protected from light. Verify the exact dating against the Body Pharm certificate of analysis shipped with your vial or pen, since lot-specific expiry can differ from the generic label claim. Brief excursions to room temperature during transit are tolerated. Sustained exposure above 25 °C measurably erodes monomer content and bioactivity.

Post-reconstitution, the working solution is stable at 2–8 °C for 28 days. Reconstitute with bacteriostatic water (0.9% benzyl alcohol) rather than sterile water if you intend to draw from the vial repeatedly. Avoid freeze-thaw cycles entirely. Each freeze-thaw fragments the 22 kDa monomer and shifts the aggregate profile, which will distort any GHR binding or hepatocyte IGF-1 induction assay downstream. The same caution applies when running parallel arms with CJC-1295 or IGF-1 LR3, where inconsistent handling between cohorts is a common confounder.

Research Notes: Cold-Chain on Arrival

JCSG.org dispatches somatropin in insulated packaging with gel cold-packs for domestic South African delivery. On receipt, confirm the cold-pack is still cool. Transfer the vial to a calibrated 2–8 °C fridge within the hour, and log the time-out-of-fridge against your batch record before the first reconstitution.

Frequently Asked Questions