Ghrelin vs IGF-1 LR3

Must be acylated at Ser3 (by GOAT enzyme) for GHSR-1a binding. Receptor activation in the pituitary stimulates GH release; hypothalamic action via NPY/AgRP neurons increases appetite and reduces energy expenditure.

Ghrelin is an endogenous 28-amino-acid peptide hormone produced primarily by X/A-like cells of the gastric fundus, characterized by a unique octanoyl modification at Ser3 required for GHS-R1a receptor binding; it is the endogenous ligand for the growth hormone secretagogue receptor and functions as a dual regulator of GH secretion and energy homeostasis. Ghrelin acts centrally via hypothalamic GHS-R1a receptors to potently stimulate GH release from the pituitary and to promote appetite through NPY/AgRP pathway activation, and has peripheral effects on gastric motility and insulin secretion, establishing it as a key integrator of nutritional status, GH axis activity, and energy balance. The pharmacology of GHS-R1a activation in humans is validated through macimorelin (Macrilen), an FDA-approved oral ghrelin receptor agonist; Phase 1 and Phase 2 randomized controlled trials of macimorelin demonstrated robust and reliable GH stimulation in adults, supporting FDA approval in 2017 for the diagnosis of adult GH deficiency and confirming the human physiological relevance of ghrelin receptor activation. Ghrelin itself is not therapeutically administered; it has a very short plasma half-life and the active acylated form is rapidly degraded in circulation; FDA-approved ghrelin receptor agonists require prescription and are indicated for diagnostic rather than therapeutic use, while ghrelin peptide is used exclusively as a research tool compound in neuroendocrine pharmacology studies.

Long-acting analog of IGF-1 that binds to IGF-1 receptors, promoting muscle protein synthesis, cellular growth, and recovery. Suppresses myostatin activity and has a significantly extended half-life compared to native IGF-1 due to reduced binding protein affinity.

IGF-1-LR3 (Long Arg3 IGF-1) is a synthetic 83-amino-acid analog of insulin-like growth factor 1, engineered with an N-terminal 13-amino-acid extension and an Arg3 substitution that substantially reduces binding to IGF-binding proteins (IGFBPs), resulting in a biological half-life approximately 120 times longer than native IGF-1 and theoretically greater receptor availability in peripheral tissues. The reduced IGFBP affinity means a higher proportion of circulating IGF-1-LR3 remains unbound and potentially bioactive; in vitro cell proliferation studies and animal models suggest amplified anabolic signaling relative to equimolar native IGF-1, and the compound is widely used as a research reagent in cell culture for controlled IGF-1R stimulation without the confounding effects of endogenous binding protein dynamics. No human pharmacokinetic, safety, or efficacy studies of IGF-1-LR3 have been published in PubMed-indexed journals; the indexed scientific literature consists of in vitro proliferation studies, animal metabolic research, and anti-doping detection methods — a complete absence of clinical data supporting or characterizing its use in humans. IGF-1-LR3 has no FDA approval or regulatory approval in any jurisdiction; it is a research laboratory reagent and non-approved analog available through research chemical suppliers, and the complete absence of published human data means its pharmacological behavior, tissue distribution, and safety profile in humans are entirely uncharacterized. IGF-1 LR3 in research contexts: as a laboratory reagent, IGF-1-LR3 is used at nanomolar concentrations in cell culture assays to stimulate IGF-1 receptor signaling. The extended half-life (approximately 20–30 hours compared to native IGF-1's 15 minutes) is the primary reason for its use in research settings requiring sustained IGF-1R activation. In animal pharmacology studies, doses vary widely by species and model; these cannot be directly extrapolated to human dosing, and no safe or effective human dose has been established. Its extended half-life relative to native IGF-1 is also the property most frequently cited in anti-doping detection literature, where the compound has been identified in biological samples from competitive athletes. The absence of any human clinical data distinguishes IGF-1-LR3 from growth hormone secretagogues such as sermorelin, ipamorelin, or MK-677, which have documented human pharmacological profiles. Providers offering researched GH-axis peptides with clinical datasets are listed in the PeptideBase directory.