GH axis, protein synthesis, body composition
Muscle growth.
Peptides investigated in preclinical and early clinical studies in the context of growth hormone secretion, muscle mass and body composition. Predominantly GH secretagogues from the GHRH and GHRP classes.
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TB-500
Thymosin Beta-4
TB-500 (as a synthetic analog of thymosin beta-4, a naturally occurring peptide) interacts with G-actin and regulates actin polymerisation in cells. Thymosin beta-4 is expressed endogenously in high concentrations in platelets and other cells and is involved in cell migration, proliferation and differentiation. Preclinical studies suggest interactions with angiogenic and inflammation-modulating signalling pathways. The term 'TB-500' is a trade designation for a synthetic fragment analog and is not identical to native thymosin beta-4.
CJC-1295
CJC 1295
CJC-1295 is a synthetic analog of the body's own growth hormone-releasing hormone (GHRH). The substance binds selectively to the GHRH receptor in the pituitary, where it stimulates the pulsatile release of growth hormone (GH). Characteristic of CJC-1295 is the DAC modification (Drug Affinity Complex): a maleimidopropionic acid group binds covalently to circulating serum albumin, thereby extending the half-life from a few minutes to several days. This produces a sustained elevation of the GH/IGF-1 baseline rather than physiological pulses. The variant without the DAC modification is listed separately as Mod GRF 1-29 and has a markedly shorter duration of action.
Ipamorelin
NNC 26-0161
Ipamorelin is a synthetic pentapeptide and a selective agonist at the ghrelin receptor (GHS-R1a). By binding to this receptor in the pituitary and hypothalamus, it stimulates the pulsatile secretion of growth hormone (GH). Compared with other GHRP compounds (e.g. GHRP-6), ipamorelin shows lower stimulation of ACTH and cortisol in preclinical studies, which has been regarded as a potential selectivity advantage — clinical confirmation is pending.
Tesamorelin
Tesamoreline
Tesamorelin is a synthetic analog of human GHRH (growth hormone-releasing hormone), consisting of the complete GHRH(1-44) peptide with a trans-3-hexenoic acid modification at the N-terminus. This modification increases stability against enzymatic degradation by dipeptidyl peptidase IV (DPP-IV). Tesamorelin stimulates pituitary GH secretion in a physiological, pulsatile manner, as it preserves the endogenous feedback regulation via IGF-1 and somatostatin. Unlike exogenous GH, the physiological regulatory mechanism remains intact.
IGF-1
Insulin-like Growth Factor 1
IGF-1 is a 70-amino-acid polypeptide with structural homology to insulin. It binds primarily to the IGF-1 receptor (IGF-1R), through which it activates the PI3K/Akt/mTOR and Ras/MAPK signalling cascades. Its main site of production is the liver, where synthesis is stimulated by growth hormone (GH). IGF-1 is regarded as a central mediator of the anabolic effects of growth hormone on muscle, bone and nerve tissue. In the blood, IGF-1 circulates bound to IGF-binding proteins (IGFBPs), which regulate its bioavailability and half-life.
IGF-1 LR3
Long R3 IGF-1
IGF-1 LR3 is a synthetically modified variant of human IGF-1. The modification comprises an N-terminal extension of 13 amino acids and the substitution of arginine with glutamic acid at position 3. These structural changes substantially reduce binding affinity to IGF-binding proteins (IGFBPs), increasing bioavailability and extending the biological half-life compared with native IGF-1 (about 12–15 minutes) to an estimated 20 hours. The mechanism of action at the IGF-1 receptor is analogous to native IGF-1: activation of the PI3K/Akt/mTOR and Ras/MAPK pathways.
GHRP-2
Pralmorelin
GHRP-2 is a synthetic hexapeptide that acts as a potent agonist at the ghrelin receptor (GHS-R1a). Binding to GHS-R1a in the somatotroph cells of the anterior pituitary triggers a strong pulsatile release of growth hormone (GH). At the same time, its hypothalamic action reduces somatostatin inhibition, further amplifying the GH pulse. Compared with GHRP-6, GHRP-2 stimulates appetite less markedly, as its ghrelinergic action on the hypothalamus is weaker. GHRP-2 also moderately raises prolactin and cortisol — an effect that can be clinically relevant at therapeutic doses.
GHRP-6
Growth Hormone Releasing Peptide-6
GHRP-6 is the first synthetic growth hormone secretagogue (GHS) and the prototype of the GHRP class. As a potent GHS-R1a agonist, it triggers pulsatile GH release from the pituitary. Characteristic of GHRP-6 is a pronounced ghrelin-mimetic effect in the hypothalamus, which, alongside GH release, mediates strong appetite stimulation via NPY and AgRP neurons. This appetite effect clinically distinguishes GHRP-6 from more selective GHRPs such as ipamorelin. GHRP-6 also raises cortisol and prolactin, more strongly than GHRP-2.
Sermorelin
GHRH(1-29)-NH₂
Sermorelin is a synthetic 29-amino-acid peptide corresponding to the first 29 amino acids of endogenous growth hormone-releasing hormone (GHRH) — the shortest sequence that still retains full biological activity at the GHRH receptor (GHRHR). By binding to GHRHR in the somatotroph cells of the anterior pituitary, sermorelin stimulates the synthesis and pulsatile release of growth hormone (GH). Compared with CJC-1295, sermorelin has a shorter biological half-life (approx. 10–20 minutes), producing more physiological, short-lived GH pulses than long-acting GHRH analogs.
Hexarelin
Examorelin
Hexarelin is a synthetic hexapeptide and the most potent GH secretagogue of the GHRP class. As a high-affinity GHS-R1a agonist, at equimolar doses it produces 2–3-fold higher GH pulses than GHRP-2, GHRP-6 or ipamorelin. In addition to GHS-R1a activity, hexarelin binds the CD36 scavenger receptor — a mechanism shown by no other GHRP compound and thought to mediate cardioprotective effects (reduction of myocardial fibrosis, improved cardiac function in animal models). Hexarelin raises cortisol and prolactin more strongly than other GHRPs and shows pronounced tachyphylaxis.
Mod GRF 1-29
Modified GRF (1-29)
Mod GRF 1-29 is a synthetic GHRH analog based on the first 29 amino acids of growth hormone-releasing hormone. Compared with sermorelin (unmodified GHRH 1-29), it carries four amino acid substitutions (D-Ala², Gln⁸, Ala¹⁵, Leu²⁷) that stabilise it against enzymatic degradation by dipeptidyl peptidase-IV (DPP-IV) and increase receptor affinity. Unlike CJC-1295 with DAC, Mod GRF 1-29 has no albumin-binding group — its half-life is therefore only about 30 minutes rather than several days. This produces a short, pulsatile GH rise that more closely resembles the physiological release pattern than the sustained baseline elevation of the DAC variant.
Somatropin (HGH)
Somatropin
Somatropin is recombinant human growth hormone (hGH), a 191-amino-acid protein that matches the body's own pituitary growth hormone in structure and action. It binds to the growth hormone receptor and mediates its effects partly directly and partly via the release of IGF-1, predominantly in the liver. Described effects include longitudinal growth (in childhood), protein synthesis, lipolysis and carbohydrate metabolism.
MGF
Mechano Growth Factor
MGF (mechano growth factor) is a splice variant of the IGF-1 gene (IGF-1 Ec) expressed mainly after mechanical muscle loading. Its characteristic C-terminal E-peptide is discussed as a separate signal thought to promote the activation and proliferation of muscle satellite cells. The pegylated form (PEG-MGF) is intended to extend the very short half-life of the native peptide. The precise receptor of the E-peptide has not been conclusively identified.
IGF-1 DES
IGF-1 DES
IGF-1 DES is a truncated variant of insulin-like growth factor 1 lacking the first three N-terminal amino acids (DES(1-3)IGF-1). This truncation makes the molecule bind much more weakly to IGF binding proteins, allowing higher relative activity at the IGF-1 receptor in tissue. In cell models an increased potency relative to full-length IGF-1 has been described. The action concerns cell proliferation, differentiation and anabolic signalling.
ACE-031
ACE-031
ACE-031 is a soluble decoy receptor: a fusion protein of the extracellular domain of activin receptor type IIB (ActRIIB) and an antibody Fc portion. It binds myostatin and related ligands before they can dock onto their cellular receptor, thereby removing their growth-inhibiting effect on muscle. An increase in muscle mass has consequently been described in studies. ACE-031 is not a classic peptide but a recombinant fusion protein.
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