Ipamorelin vs Tesamorelin

Ipamorelin

Ipamorelin is a synthetic pentapeptide, Aib-His-D-2-Nal-D-Phe-Lys-NH2, that acts as an agonist at the ghrelin receptor, GHS-R1a. It was derived from earlier growth hormone-releasing peptides and is one residue shorter than GHRP-2 and GHRP-6. What set it apart in the original animal pharmacology was selectivity: growth hormone release was not accompanied by the rises in ACTH and cortisol recorded for older compounds in the class. Because ghrelin receptors are also present in the gut, it has been examined in rodent models of gastrointestinal motility, and it has been the subject of a small number of human clinical studies. Human data remain limited, and most of what is known comes from animal work.

Tesamorelin

Tesamorelin is a modified form of human growth hormone-releasing hormone (GHRH), keeping all 44 residues but altering the N-terminus. A trans-3-hexenoyl group is attached to the first residue, tyrosine, a change reported to shield the peptide from dipeptidyl peptidase-4, the enzyme that inactivates native GHRH within minutes. That distinguishes it from sermorelin, which keeps only the first 29 residues and carries no protecting group. Human clinical research has concentrated on HIV-associated lipodystrophy, a condition involving abnormal fat distribution, with smaller studies in other areas. Animal and cell work on the growth hormone axis sits alongside this, but outside the lipodystrophy setting, human data are limited.

How Ipamorelin acts

Ipamorelin has been reported to bind GHS-R1a on somatotroph cells of the anterior pituitary, where receptor activation raises intracellular calcium and triggers growth hormone secretion. Its reported selectivity concerns other pituitary and adrenal hormones: in the animal studies that first characterised it, ACTH and cortisol did not rise appreciably, unlike with GHRP-6 or GHRP-2. The structural basis for this difference has not been fully explained. The receptor is also found in the gut wall and its nerve supply, which is the rationale for rodent studies of gastrointestinal transit using this compound.

How Tesamorelin acts

Tesamorelin binds the GHRH receptor on somatotroph cells of the anterior pituitary, the class B G-protein-coupled receptor also targeted by native GHRH and sermorelin. Receptor activation raises cyclic AMP and has been reported to increase both synthesis and release of growth hormone, which keeps a pulsatile pattern because somatostatin and IGF-1 feedback still operate. Circulating growth hormone in turn drives IGF-1 production, mostly in the liver. Studies of adipose tissue have examined the lipolytic action of growth hormone as one link in this pathway, though the separate roles of growth hormone and IGF-1 are not fully resolved.

The records side by side

• Type: Ipamorelin, Growth hormone secretagogue (GHRP); Tesamorelin, GHRH analog (growth hormone secretagogue)
• Length: Ipamorelin, 5 amino acids; Tesamorelin, 44 amino acids
• Molecular weight: Ipamorelin, 711.9 g/mol; Tesamorelin, 5136 g/mol
• Molecular formula: Ipamorelin, C38H49N9O5; Tesamorelin, C221H366N72O67S
• Half-life: Ipamorelin, not recorded; Tesamorelin, Mean elimination half-life (T1/2) of tesamorelin was 26 and 38 minutes in healthy subjects and HIV-infected patients, respectively, after subcutaneous administration for 14 consecutive days." (original EGRIFTA label, 2010). By contrast t…

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.