Radiolabeled ghrelin bound to human hypothalamus and pituitary with high affinity but showed a different binding profile than synthetic GH secretagogues like hexarelin, suggesting receptor subtypes or binding modes differ.
Different binding profilesGhrelin and synthetic GH secretagogues bind human brain tissue differently — the receptor system is more complex than assumed
What the researchers found
125I-ghrelin bound to human hypothalamus and pituitary with high affinity but showed different binding characteristics than synthetic GHS (hexarelin, MK-0677), suggesting distinct receptor interaction modes or subtypes.
Why it matters
If ghrelin and synthetic GH secretagogues bind differently, they could have distinct therapeutic profiles. This explains why ghrelin (appetite + GH) and some synthetic GHS (GH-selective like ipamorelin) have different effect spectra.
How the study worked
In-vitro binding study using 125I-labeled ghrelin on human hypothalamic and pituitary membrane preparations. Competition binding with unlabeled ghrelin, hexarelin, and MK-0677 to characterize binding sites.
What this study cannot tell us
In-vitro binding on post-mortem tissue. Binding differences don't conclusively prove separate receptor subtypes. Human tissue availability limits sample size.
How to read the evidence
Preliminary in-vitro binding evidence in human tissue providing receptor pharmacology data suggesting system complexity.
When this study was published
Published in 2001. GHS receptor complexity has been further characterized, with constitutive activity and heterodimerization adding additional complexity.
The bigger picture
The GH secretagogue receptor system is more complex than a single receptor. Different binding modes for the natural ligand versus designed drugs could explain the diversity of effects seen with different compounds.
Questions still open
- Do multiple GHS receptor subtypes exist in the human brain?
- Does the binding difference explain ghrelin's appetite effect versus synthetic GHS's selectivity?
- Can subtype-selective drugs be developed from this binding data?
Common questions
Don't all GH peptides work the same way?
What does this mean for choosing a GH peptide?
Read the original research
Binding of 125I-labeled ghrelin to membranes from human hypothalamus and pituitary gland.
Journal of endocrinological investigation, 24(3), RC7-9
Citation
Muccioli, G; Papotti, M; Locatelli, V; Ghigo, E; Deghenghi, R. (2001). Binding of 125I-labeled ghrelin to membranes from human hypothalamus and pituitary gland.. Journal of endocrinological investigation, 24(3), RC7-9.