GHRP-2 vs Sermorelin

GHRP-2

GHRP-2, also known by the non-proprietary name pralmorelin, is a synthetic hexapeptide that activates the ghrelin receptor, GHS-R1a. Three of its six residues are D-amino acids, including the non-natural D-2-naphthylalanine, a design feature shared with other synthetic growth hormone-releasing peptides. These compounds were developed by screening for growth hormone release before their receptor had been identified; ghrelin, the receptor's natural ligand, was discovered afterwards. GHRP-2 has been examined in receptor and pituitary cell assays, in animal studies, and in short human endocrine studies that measured hormone secretion. Longer-term human data are sparse, and it is not selective for growth hormone, since rises in other pituitary and adrenal hormones have also been recorded.

Sermorelin

Sermorelin is a synthetic 29-residue peptide reproducing the N-terminal segment of human growth hormone-releasing hormone (GHRH). Native GHRH has 44 residues, and the 1–29 segment, amidated at its C-terminus as here, is reported to retain the receptor activity of the full hormone. Like native GHRH, it is cut quickly by plasma enzymes including dipeptidyl peptidase-4, a property that later analogues such as tesamorelin were modified to avoid. Research on it has centred on growth hormone release from the anterior pituitary, including human physiology studies, many of them decades old, alongside animal and cell work. Recent literature on sermorelin itself is sparse beside that on newer GHRH analogues.

How GHRP-2 acts

GHRP-2 has been reported to act as an agonist at GHS-R1a, a G protein-coupled receptor present on somatotroph cells of the anterior pituitary and on neurons in the hypothalamus. In somatotrophs the receptor couples mainly to Gq and phospholipase C, and the rise in intracellular calcium that follows triggers growth hormone secretion. This route is separate from that of growth hormone-releasing hormone (GHRH), which acts through its own receptor and cyclic AMP. Part of the response is thought to be hypothalamic, through effects on GHRH neurons and on somatostatin signalling. In human studies, modest increases in ACTH, cortisol and prolactin have been reported alongside growth hormone.

How Sermorelin acts

Sermorelin binds the GHRH receptor, a class B G-protein-coupled receptor on somatotroph cells of the anterior pituitary. Receptor activation has been reported to raise cyclic AMP and activate protein kinase A and the transcription factor CREB, which is linked to transcription of the growth hormone gene as well as to release of stored hormone. Because it acts upstream of the pituitary, the growth hormone released stays subject to inhibition by somatostatin and to negative feedback from IGF-1. This is the main pharmacological difference between GHRH analogues and growth hormone itself.

The records side by side

• Type: GHRP-2, Growth hormone secretagogue (GHRP); Sermorelin, GHRH analog (growth hormone secretagogue)
• Length: GHRP-2, 6 amino acids; Sermorelin, 29 amino acids
• Molecular weight: GHRP-2, 818.0 g/mol; Sermorelin, 3357.9 g/mol
• Molecular formula: GHRP-2, C45H55N9O6; Sermorelin, C149H246N44O42S

Reading a comparison

A comparison places two records side by side; it does not merge them. Each description above is drawn from that compound's own record, and the two were not necessarily characterised by the same methods, at the same time, or to the same level of detail. Before comparing any attribute, it is worth establishing that both records describe the substance you think they describe — names are not identifiers, and two entries sharing a name can differ in salt form, stereochemistry or the convention used to state a mass. Where a figure carries no method beside it, the comparison is between two reported numbers rather than between two measurements.