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The Growth Hormone Secretagogue Receptor Family: From Orphan Receptor to Ghrelin Discovery

RPEP-006992001Smith, R G; Leonard, R; Bailey, A R; Palyha, O; Feighner, S; Tan, C; Mckee, K K; Pong, S S; Griffin, P; Howard, A
In VitroPreliminary evidence
The takeaway

Characterization of the GHS-R family revealed a constitutively active receptor with ghrelin as its natural ligand and a related receptor (GHS-R1b) whose function remains unknown, mapping the complete receptor system.

Always on

The ghrelin receptor signals even without ghrelin — this constitutive activity may drive baseline hunger and represents a unique drug target

What the researchers found

The GHS-R family includes the active GHS-R1a (ghrelin receptor, constitutively active) and the orphan GHS-R1b splice variant, with constitutive activity suggesting baseline signaling roles and inverse agonist therapeutic potential.

Why it matters

Constitutive activity means the ghrelin receptor signals even when ghrelin isn't present. This has implications for appetite regulation (baseline hunger signaling) and drug development (inverse agonists could reduce this baseline signal for appetite suppression).

How the study worked

In-vitro receptor characterization using cloned GHS-R1a and GHS-R1b. Binding, signaling, and constitutive activity assessed in expression systems.

What this study cannot tell us

In-vitro characterization. GHS-R1b's function remains undetermined. Constitutive activity in expression systems may differ from native tissue.

How to read the evidence

Preliminary receptor characterization from the group that cloned GHS-R, providing authoritative data on the complete receptor family.

When this study was published

Published in 2001. GHS-R1a constitutive activity has been confirmed and is now targeted by inverse agonist drug candidates for obesity.

The bigger picture

Constitutively active receptors change the therapeutic landscape — you can not only activate them (agonists) or block them (antagonists) but also suppress their baseline activity (inverse agonists). For the hunger receptor, this could mean true appetite suppression.

Questions still open

  • Do inverse agonists at GHS-R1a suppress appetite?
  • What is GHS-R1b's function?
  • Does constitutive GHS-R1a activity contribute to baseline hunger?

Common questions

What does a constitutively active receptor mean?
Most receptors sit quietly until a hormone activates them. The ghrelin receptor is different — it's always partially active, sending a constant low-level hunger signal. This may explain baseline appetite drive.
Could this help treat obesity?
Yes. Inverse agonists — drugs that suppress the receptor's baseline activity — could reduce the constant hunger signal. This is a fundamentally different approach from simply blocking ghrelin binding.

Read the original research

Growth hormone secretagogue receptor family members and ligands.

Endocrine, 14(1), 9-14

View on PubMed ↗

Citation

Smith, R G; Leonard, R; Bailey, A R; Palyha, O; Feighner, S; Tan, C; Mckee, K K; Pong, S S; Griffin, P; Howard, A. (2001). Growth hormone secretagogue receptor family members and ligands.. Endocrine, 14(1), 9-14.