MGF (Mechano Growth Factor, IGF-1Ec)

1. Overview

Mechano Growth Factor (MGF) is a splice variant of the insulin-like growth factor 1 (IGF-1) gene that is expressed in response to mechanical loading and tissue damage in skeletal muscle, cardiac muscle, bone, and other mechanosensitive tissues. In humans, MGF corresponds to the IGF-1Ec splice variant (IGF-1Eb in rodents), distinguished from the predominant circulating form (IGF-1Ea) by alternative splicing of exons 5 and 6 of the IGF-1 gene, which produces a unique 24-amino acid C-terminal extension peptide (the E-peptide or Ec peptide) [1][2][3].

The discovery and characterization of MGF is primarily attributed to Professor Geoffrey Goldspink and colleagues at University College London and the Royal Free Hospital, who demonstrated in the late 1990s and early 2000s that mechanical stretch of skeletal muscle induced rapid, transient expression of a specific IGF-1 splice variant that preceded and was distinct from the sustained IGF-1Ea expression [3]. They named this variant "Mechano Growth Factor" to reflect its mechanical stimulus-dependent expression and proposed that it represents a local autocrine/paracrine repair signal that initiates the early regenerative response to muscle damage or exercise [2][7].

The key biological insight was that the unique E-peptide of MGF appears to have independent biological activity separate from the mature IGF-1 peptide that is produced after post-translational processing. Yang and Goldspink (2002) demonstrated that the MGF E-peptide alone -- without the mature IGF-1 moiety -- could activate quiescent satellite (muscle stem) cells and promote myoblast proliferation, while the mature IGF-1 peptide (common to all IGF-1 isoforms) primarily drove myoblast differentiation and fusion [1]. This temporal and functional division of labor -- MGF for initial satellite cell activation, IGF-1Ea for subsequent differentiation -- established the "two-phase" model of IGF-1 splice variant function in muscle repair [2][7].

Synthetic peptides corresponding to the 24-amino acid MGF E-domain are available as research compounds. Because the unmodified synthetic E-peptide is extremely rapidly degraded in serum (half-life approximately 5-7 minutes), a PEGylated variant (PEG-MGF) has been developed to extend biological activity, with a half-life of several hours. Neither form has been tested in human clinical trials, and MGF has no approved therapeutic use in any jurisdiction.

Type

Splice variant of IGF-1 gene (IGF-1Ec in humans)

E-Peptide Sequence

24 amino acids unique to MGF (encoded by exon 5/6 reading frame)

Gene

IGF1 (chromosome 12q23.2)

Expression Trigger

Mechanical loading, exercise, muscle damage

Primary Action

Satellite cell activation and myoblast proliferation

Half-life (synthetic)

~5-7 minutes (unmodified); ~several hours (PEG-MGF)

FDA Status

Not approved; research compound only

WADA Status

Prohibited at all times (S2: Peptide Hormones, Growth Factors)

2. Molecular Biology and Splicing

2.1 IGF-1 Gene Structure

The human IGF-1 gene is located on chromosome 12q23.2 and spans approximately 90 kb. It contains six exons that undergo complex alternative splicing to produce multiple mRNA transcripts encoding different IGF-1 precursor proteins. All transcripts share exons 3 and 4, which encode the mature 70-amino acid IGF-1 peptide (B, C, A, and D domains) common to all isoforms. The biological diversity arises from differential inclusion of exons 1/2 (alternative leader sequences and signal peptides) and exons 5/6 (alternative E-peptides) [2][12][18].

2.2 IGF-1 Splice Variants

Three principal E-peptide variants are produced in humans [2][12][18]:

IGF-1Ea (predominant systemic form): Exons 1/2 - 3 - 4 - 6. The Ea peptide (35 amino acids in humans) is the default E-domain. This is the primary hepatic isoform produced under GH stimulation and is processed to yield the mature circulating IGF-1 that mediates the endocrine growth-promoting actions of the GH/IGF-1 axis.

IGF-1Eb (minor variant): Exons 1/2 - 3 - 4 - 5 - 6 (partial exon 5 inclusion). A minor splice variant in humans with limited characterization.

IGF-1Ec (MGF in humans): Exons 1/2 - 3 - 4 - 5 - 6 (frame-shifted exon 5 inclusion producing a unique 24-aa C-terminal reading frame from the exon 5/6 junction). The Ec peptide sequence in humans is: Tyr-Gln-Pro-Pro-Ser-Thr-Asn-Lys-Asn-Thr-Lys-Ser-Gln-Arg-Arg-Lys-Gly-Ser-Thr-Phe-Glu-Glu-His-Lys (24 amino acids). Note that in rodents, the equivalent variant is designated IGF-1Eb rather than IGF-1Ec due to differences in gene structure [2][18].

2.3 Expression Pattern

The expression kinetics of MGF are fundamentally different from IGF-1Ea [3][5]:

MGF (IGF-1Ec): Rapidly upregulated within 1-2 hours after mechanical loading or tissue damage. Expression peaks at approximately 2-6 hours and returns to baseline within 24-72 hours. This transient "pulse" of MGF is believed to initiate the repair cascade by activating quiescent satellite cells.

IGF-1Ea: Expression rises more slowly, peaking at 24-72 hours post-stimulus and remaining elevated for days to weeks. IGF-1Ea drives the sustained phase of muscle repair, including myoblast differentiation, fusion into myotubes, and protein synthesis.

Hameed et al. (2003) confirmed this temporal pattern in human skeletal muscle, demonstrating that MGF mRNA was significantly elevated 2.5 hours after acute resistance exercise in young men, preceding the rise in IGF-1Ea expression [5].

3. Mechanism of Action

3.1 The Two-Phase Model

The prevailing model proposed by Goldspink and colleagues posits that MGF and IGF-1Ea serve complementary but temporally distinct functions in muscle repair [1][2][7]:

Phase 1 (MGF/Satellite Cell Activation, 0-24 hours):

• Mechanical loading or damage triggers rapid MGF transcription via mechanosensitive transcription factors
• The IGF-1Ec precursor protein is produced and proteolytically processed
• The released MGF E-peptide activates quiescent satellite cells (residing between the sarcolemma and basal lamina), driving them from G0 into the cell cycle
• MGF E-peptide promotes satellite cell proliferation without premature differentiation
• MGF E-peptide also inhibits myoblast apoptosis, preserving the regenerative cell pool

Phase 2 (IGF-1Ea/Differentiation and Hypertrophy, 24+ hours):

• MGF expression declines as IGF-1Ea expression rises
• Mature IGF-1 released from IGF-1Ea precursor processing drives myoblast differentiation, fusion, and myotube formation
• IGF-1 activates the PI3K/Akt/mTOR pathway, stimulating protein synthesis and promoting myofiber hypertrophy

3.2 E-Peptide Signaling

The MGF E-peptide appears to signal through a receptor or mechanism distinct from the IGF-1 receptor (IGF-1R). Key evidence for this includes [1][4]:

• The E-peptide alone (without mature IGF-1) can activate satellite cells and promote myoblast proliferation
• The mature IGF-1 peptide (common to all splice variants) drives differentiation rather than proliferation
• The E-peptide does not compete for IGF-1R binding
• Anti-IGF-1R antibodies do not fully block E-peptide-mediated satellite cell activation

The specific receptor or binding partner for the MGF E-peptide has not been definitively identified, though some evidence suggests involvement of extracellular matrix interactions, membrane-associated receptors, or intracellular signaling after cellular uptake. The E-peptide contains a polybasic motif (Arg-Arg-Lys-Gly-Ser) that may facilitate cell-penetrating peptide-like internalization.

3.3 Anti-Apoptotic Activity

The MGF E-peptide has demonstrated anti-apoptotic effects in multiple cell types. In C2C12 myoblasts subjected to oxidative stress (hydrogen peroxide), synthetic MGF E-peptide reduced apoptosis through activation of the p38 MAPK pathway and inhibition of caspase-3 activity. In neuronal cells, the E-peptide provided neuroprotection against ischemic and traumatic injury, reducing neuronal apoptosis and improving functional outcomes [10][11][15].

3.4 Cardiac Actions

MGF (IGF-1Ec) is rapidly upregulated in cardiac tissue following myocardial infarction, with expression peaking at approximately 3 days post-MI [8][9]. Carpenter et al. (2008) demonstrated that MGF E-peptide reduced the loss of cardiac function following acute MI in a rat model, potentially through anti-apoptotic protection of cardiomyocytes in the peri-infarct zone and activation of cardiac progenitor cells [9].

4. Researched Applications

4.1 Skeletal Muscle Repair and Hypertrophy

Evidence level: Preclinical

The primary proposed application for MGF is acceleration of skeletal muscle repair following injury or exercise-induced damage. Goldspink et al. (2004) demonstrated that a single intramuscular injection of synthetic MGF E-peptide (50 ng per muscle) into damaged mouse muscle accelerated the regenerative process by approximately 25% and increased muscle fiber cross-sectional area by 20% compared to controls [7].

Hill and Goldspink (2003) showed that the MGF E-peptide activated satellite cells in a dose-dependent manner in vitro, increasing the population of proliferating myogenic precursors available for muscle repair [4]. Mills et al. (2007) demonstrated that synthetic MGF E-peptide enhanced the success of myogenic precursor cell transplantation, improving engraftment and survival of transplanted cells [17].

4.2 Age-Related Muscle Loss (Sarcopenia)

Evidence level: Preclinical / observational human data

A potentially significant finding is the age-related decline in MGF expression capacity. Owino, Yang, and Goldspink (2001) demonstrated that aged rodent muscle had a markedly blunted MGF response to mechanical overload compared to young muscle, while IGF-1Ea expression was less affected [13]. Hameed et al. (2005) confirmed this in humans, showing that MGF mRNA induction following resistance exercise was significantly attenuated in older men (65-75 years, 1.8-fold increase) compared to young men (25-35 years, 5.0-fold increase) [6 (study in quickfacts)].

This age-related loss of MGF responsiveness may contribute to the impaired satellite cell activation, reduced regenerative capacity, and progressive muscle loss characteristic of sarcopenia. The finding also suggests that exogenous MGF supplementation could theoretically restore the diminished repair capacity of aged muscle, though this remains speculative.

4.3 Cardiac Repair

Evidence level: Preclinical

The rapid upregulation of MGF in cardiac tissue following myocardial infarction [8] and the demonstration that MGF E-peptide can reduce cardiac functional loss in rodent MI models [9] suggest a role in cardiac repair. The proposed mechanism involves anti-apoptotic protection of cardiomyocytes in the peri-infarct zone and potential activation of cardiac progenitor cells. However, this area of research remains early-stage with no clinical translation.

4.4 Neuroprotection

Evidence level: Preclinical

MGF E-peptide has demonstrated neuroprotective effects in rodent models of both cerebral ischemia and traumatic brain injury. Dluzniewska et al. (2005) showed that the autonomous C-terminal peptide of IGF-1Ec (the MGF E-peptide) provided strong neuroprotection against brain ischemia in rats [10]. In a traumatic brain injury model, intracerebroventricular MGF E-peptide reduced neuronal apoptosis by approximately 45%, decreased cortical lesion volume, and improved behavioral recovery [11]. Aperghis et al. (2004) demonstrated that MGF provided different neuroprotective characteristics compared to IGF-1Ea, supporting distinct biological activities of the splice variants [15].

4.5 Bone Repair and Mechanotransduction

Evidence level: Preclinical

MGF is expressed in osteoblasts and osteocytes following mechanical loading of bone. Tang et al. (2007) showed that MGF mRNA was rapidly upregulated within 6 hours of controlled mechanical loading of rat tibiae, preceding IGF-1Ea expression [16]. This temporal pattern mirrors the muscle response and suggests that MGF plays a role in the mechanotransduction pathway that links mechanical stimulation to bone formation, potentially through activation of osteogenic progenitor cells.

5. Clinical Evidence Summary

6. Dosing in Research

The following table summarizes doses used in published preclinical research. No human clinical trials have been conducted with synthetic MGF or PEG-MGF. These are not therapeutic recommendations.

7. Safety and Side Effects

7.1 Limited Safety Data

No systematic safety studies or human clinical trials have been conducted with synthetic MGF or PEG-MGF. Safety assessment relies entirely on preclinical observations and theoretical extrapolation from IGF-1 biology.

7.2 Rapid Degradation of Unmodified MGF

The extremely short half-life of synthetic MGF E-peptide (approximately 5-7 minutes in serum) presents both a practical limitation and an inherent safety feature. The peptide is rapidly degraded by serum proteases, limiting systemic exposure following local administration. However, this also means that achieving therapeutic concentrations requires either local injection at the target site, continuous infusion, or use of the stabilized PEG-MGF variant.

7.3 PEG-MGF Considerations

PEGylation (polyethylene glycol conjugation) of the MGF E-peptide extends its half-life to several hours, enabling subcutaneous or intramuscular administration with systemic bioavailability. While PEGylation is a well-established pharmaceutical strategy, PEG-MGF specifically has not undergone toxicological evaluation, and the extended exposure window introduces greater potential for off-target effects compared to the rapidly cleared unmodified peptide.

7.4 Theoretical Concerns

Satellite cell depletion: Chronic exogenous satellite cell activation could theoretically exhaust the satellite cell pool through repeated proliferative cycling, reducing long-term regenerative capacity. This concern has been raised for any intervention that repeatedly drives satellite cells into the cell cycle.

Oncogenic potential: While the MGF E-peptide has not been directly linked to oncogenesis, its proliferative and anti-apoptotic properties could theoretically promote tumor growth or survival, particularly in tissues with pre-existing neoplastic lesions. The E-peptide's ability to activate quiescent progenitor cells raises the question of whether it could also activate dormant cancer stem cells.

Cardiac effects: The anti-apoptotic and cell-activating properties that are therapeutically desirable in the acute post-MI setting could be counterproductive if chronically maintained, potentially promoting cardiac fibrosis or arrhythmogenic remodeling.

7.5 Regulatory and Anti-Doping Status

MGF is prohibited at all times by WADA under category S2 (Peptide Hormones, Growth Factors, Related Substances, and Mimetics) [19]. It has no approved therapeutic use in any jurisdiction. Products available through the research peptide market are unregulated and may contain impurities, degradation products, or incorrect concentrations.

8. PEG-MGF

8.1 Rationale

The primary limitation of synthetic MGF E-peptide as a research tool or potential therapeutic is its extremely rapid degradation. PEGylation addresses this by covalently attaching a polyethylene glycol chain to the peptide, which:

• Increases hydrodynamic radius, reducing renal filtration
• Shields the peptide from proteolytic enzymes
• Extends circulating half-life from approximately 5-7 minutes to several hours

8.2 Biological Activity

PEG-MGF retains the satellite cell-activating and proliferative properties of the unmodified E-peptide. In mouse studies, PEG-MGF produced measurable muscle hypertrophy following intramuscular injection, with effects sustained over days rather than the minutes of activity achievable with unmodified MGF. The longer-acting profile enables less frequent dosing and greater systemic distribution.

8.3 Limitations

PEG-MGF has been characterized almost exclusively in preclinical and cell culture systems. No pharmacokinetic, pharmacodynamic, or toxicological data from human studies exist. The PEG conjugation site, PEG molecular weight, and linker chemistry vary between different research preparations, introducing significant batch-to-batch variability in unregulated products.

9. MGF in the Context of the GH/IGF-1 Axis

MGF occupies a unique position in the GH/IGF-1 axis as a local, mechano-responsive signal that functions independently of the classical endocrine pathway:

• Endocrine IGF-1 (IGF-1Ea): Produced primarily by the liver under GH stimulation. Circulates bound to IGFBP-3/ALS ternary complex. Mediates systemic growth-promoting effects.
• Autocrine/paracrine MGF (IGF-1Ec): Produced locally in mechanically stimulated tissues. The E-peptide has independent activity. Functions as an immediate-early repair signal rather than a sustained growth factor.

This distinction means that MGF biology is not simply "more IGF-1" -- the E-peptide acts through different pathways to achieve different biological outcomes (proliferation vs. differentiation), and the temporal expression pattern ensures orderly progression of the repair cascade from satellite cell activation through myofiber maturation [2][7][18].

10. Pharmacokinetics

The pharmacokinetics of synthetic MGF E-peptide are dominated by its extremely rapid degradation by serum peptidases, which has driven development of the PEGylated variant (PEG-MGF) [2][7].

Unmodified MGF E-peptide. The synthetic 24-amino acid E-peptide has an estimated serum half-life of approximately 5-7 minutes. This extremely short half-life results from rapid cleavage by serum and tissue peptidases, particularly at the multiple basic residues (Arg-Arg-Lys, Lys-Asn-Thr-Lys) within the sequence. The peptide is too small (approximately 2.7 kDa) for significant plasma protein binding and is rapidly filtered and catabolized by the kidneys.

PEG-MGF. PEGylation (conjugation of polyethylene glycol) extends the half-life from minutes to several hours through: (1) increased hydrodynamic radius reducing renal filtration; (2) steric shielding from proteolytic enzymes; (3) reduced immunogenicity. PEG-MGF retains satellite cell activation capacity while enabling subcutaneous or intramuscular administration with systemic distribution. The specific PEG molecular weight, conjugation site, and linker chemistry vary between preparations, introducing batch-to-batch variability in unregulated products.

Route-dependent PK. The endogenous MGF system is autocrine/paracrine -- the E-peptide is produced locally in mechanically stimulated tissue and acts on nearby satellite cells. This means the physiological "delivery" is direct tissue production, not systemic circulation. Synthetic intramuscular injection of MGF at the target muscle partially mimics this local delivery. Subcutaneous injection of PEG-MGF provides systemic distribution, which is non-physiological and distributes the peptide to all tissues rather than the target muscle.

Absorption. Intramuscular injection delivers the peptide directly to the tissue of interest but with rapid degradation limiting the effective exposure window to minutes (unmodified) or hours (PEG-MGF). Subcutaneous absorption kinetics for PEG-MGF have not been formally characterized.

Comparison with endogenous MGF kinetics. Endogenous MGF (IGF-1Ec) mRNA is transiently expressed 1-6 hours post-stimulus and returns to baseline within 24-72 hours. The E-peptide released from precursor processing would act locally in a paracrine fashion. This transient pulse is believed to be functionally important -- sustained MGF expression does not occur physiologically, and the shift from MGF to IGF-1Ea expression is part of the ordered repair cascade [3][5].

Practical implications. The extremely short half-life of unmodified MGF limits its utility as an exogenous therapeutic. Achieving even brief exposure requires direct local injection at the target site. PEG-MGF addresses this limitation but introduces a non-physiological sustained exposure pattern that may disrupt the normal temporal sequence of muscle repair (MGF pulse followed by IGF-1Ea sustained expression).

11. Dose-Response Relationship

Satellite cell activation dose-response. Hill and Goldspink (2003) demonstrated dose-dependent satellite cell activation by MGF E-peptide in vitro (C2C12 myoblasts), with increasing concentrations from 10-100 ng/mL driving progressively greater proliferation of myogenic precursors without premature differentiation [4]. Yang and Goldspink (2002) confirmed that the E-peptide alone (without mature IGF-1) activated satellite cells in a concentration-dependent manner [1].

In vivo muscle repair dose-response. Goldspink et al. (2004) showed that a single intramuscular injection of 50 ng synthetic MGF E-peptide into damaged mouse muscle accelerated regeneration by approximately 25% and increased muscle fiber cross-sectional area by 20% [7]. The low dose (50 ng) suggests high local potency when delivered directly to the target tissue.

Anti-apoptotic dose-response. In C2C12 myoblasts subjected to oxidative stress, MGF E-peptide provided dose-dependent protection against hydrogen peroxide-induced apoptosis through p38 MAPK activation and caspase-3 inhibition. Protective effects were observed at concentrations as low as 10 ng/mL.

Neuroprotective dose-response. Intracerebroventricular injection of 50 mcg MGF E-peptide reduced neuronal apoptosis by approximately 45% and decreased cortical lesion volume following TBI in rats [11]. Dluzniewska et al. (2005) demonstrated neuroprotection in brain ischemia models [10].

Age-related blunting. The endogenous MGF dose-response is significantly attenuated with aging. Hameed et al. (2005) showed that MGF mRNA induction after resistance exercise was approximately 3-fold lower in older men (65-75 years, 1.8-fold increase) compared to young men (25-35 years, 5.0-fold increase), suggesting that age-related sarcopenia may partly result from insufficient MGF signaling [6 in studies].

PEG-MGF dose-response. In mouse studies, PEG-MGF at 100-500 mcg/kg produced measurable muscle hypertrophy with effects sustained over days. The dose-response relationship for PEG-MGF has not been formally characterized in dose-ranging studies.

No human dose-response data. Neither MGF nor PEG-MGF has been studied in humans. Community-reported doses have no scientific basis.

12. Comparative Effectiveness

MGF vs IGF-1 (mature peptide). MGF E-peptide and mature IGF-1 serve complementary but temporally distinct roles in the two-phase model of muscle repair. MGF activates quiescent satellite cells (proliferation without differentiation, Phase 1), while mature IGF-1 drives differentiation, fusion, and hypertrophy (Phase 2). They signal through different receptors/pathways -- the MGF E-peptide does not bind IGF-1R, and anti-IGF-1R antibodies do not fully block E-peptide effects [1][4]. The two are not interchangeable but rather sequential components of a coordinated repair cascade.

MGF vs PEG-MGF. PEG-MGF extends the half-life from approximately 5-7 minutes to several hours, enabling practical subcutaneous administration and systemic distribution. PEG-MGF retains satellite cell activation capacity. However, the sustained exposure pattern of PEG-MGF is non-physiological -- endogenous MGF expression is a transient pulse (hours, not days), and sustained exposure could disrupt the normal temporal transition from proliferation to differentiation.

MGF vs IGF-1 LR3. Different mechanisms and applications. IGF-1 LR3 provides sustained IGF-1R activation (anabolic signaling, protein synthesis, anti-apoptosis via PI3K/Akt/mTOR). MGF E-peptide activates satellite cells through an IGF-1R-independent mechanism and promotes proliferation rather than differentiation. For muscle repair, the theoretical optimal approach would combine early MGF (satellite cell activation) followed by IGF-1 LR3 (sustained anabolic signaling for differentiation and hypertrophy) -- though this has not been formally tested.

MGF vs exogenous GH. GH indirectly stimulates both MGF and IGF-1Ea expression in muscle. Exogenous GH administration in elderly men does increase local IGF-1 mRNA but the MGF response remains blunted compared to young subjects. Direct MGF supplementation could theoretically bypass this age-related bottleneck, though this remains speculative [6 in studies][13].

MGF vs exercise. Resistance exercise is the primary physiological stimulus for endogenous MGF expression. A single bout of high-intensity resistance exercise produces a 2.5-5 fold increase in MGF mRNA within 2.5 hours in young adults. Exercise provides the full temporal sequence (MGF pulse followed by sustained IGF-1Ea), appropriate local delivery, and concurrent mechanical and hormonal stimuli. Exogenous MGF cannot replicate this integrated response [5].

13. Enhanced Safety Profile

No human safety data. Neither synthetic MGF E-peptide nor PEG-MGF has been tested in human clinical trials. All safety assessment relies on preclinical observations and theoretical extrapolation.

Rapid degradation as safety feature (unmodified MGF). The approximately 5-7 minute serum half-life of unmodified MGF provides an inherent safety margin: any adverse effects from local injection would be transient. Systemic exposure is negligible with intramuscular injection due to rapid degradation.

PEG-MGF extended exposure risk. PEGylation extends exposure from minutes to hours, enabling systemic distribution and accumulation with repeated dosing. While this is desirable for efficacy, it removes the safety margin of rapid clearance and introduces prolonged signaling to non-target tissues.

Satellite cell depletion concern. Chronic exogenous satellite cell activation could theoretically exhaust the satellite cell pool through repeated forced proliferative cycling. Satellite cells have a finite replicative capacity, and premature depletion could paradoxically reduce long-term regenerative potential. This concern applies to any intervention (including chronic intense training) that repeatedly drives satellite cell entry into the cell cycle.

Oncogenic potential. The proliferative and anti-apoptotic properties of the MGF E-peptide (satellite cell activation, caspase-3 inhibition, p38 MAPK activation) could theoretically promote tumor growth or survival, particularly in tissues harboring pre-existing neoplastic lesions or dormant cancer stem cells. No carcinogenicity studies have been conducted.

Cardiac safety considerations. While MGF shows promise for acute cardiac repair (anti-apoptotic protection of peri-infarct cardiomyocytes), chronic or inappropriate cardiac MGF exposure could promote fibrosis, arrhythmogenic remodeling, or pathological hypertrophy. The therapeutic window for cardiac applications is likely narrow and timing-dependent [9].

Research peptide quality. Products from unregulated sources carry risks of endotoxin contamination, degradation products (the multiple basic residues make MGF prone to cleavage), and inaccurate concentrations. PEG-MGF preparations vary in PEG molecular weight, conjugation site, and linker chemistry, producing significant batch-to-batch variability.

WADA prohibition. MGF is prohibited at all times under S2 (Peptide Hormones, Growth Factors, Related Substances, and Mimetics) [19].

Theoretical interaction with exercise. Exogenous MGF administered around the time of exercise could potentially interfere with the normal temporal sequence of repair (MGF pulse followed by IGF-1Ea for differentiation). Sustained or mistimed MGF exposure could maintain satellite cells in a proliferative state, delaying the differentiation and fusion steps necessary for functional muscle repair.

14. Related Peptides

See also: IGF-1 LR3 (Long R3 IGF-1), IGF-1 DES (Des(1-3) IGF-1), Human Growth Hormone (hGH), HGH Fragment 176-191, Follistatin-344, BPC-157, TB-500 (Thymosin Beta-4)

15. References

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3. [3] McKoy G, Ashley W, Mander J, et al. (1999). Expression of insulin growth factor-1 splice variants and structural genes in rabbit skeletal muscle induced by stretch and stimulation. J Physiol. DOI PubMed
4. [4] Hill M, Goldspink G. (2003). Expression and splicing of the insulin-like growth factor gene in rodent muscle is associated with muscle satellite (stem) cell activation following local tissue damage. J Physiol. PubMed
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10. [10] Dluzniewska J, Sarnowska A, Beresewicz M, et al. (2005). A strong neuroprotective effect of the autonomous C-terminal peptide of IGF-1 Ec (MGF) in brain ischemia. FASEB J. PubMed
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