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In Chickens, Ghrelin Does the Opposite: It DECREASES Appetite Instead of Increasing It

RPEP-007652002Saito, Ei-suke; Kaiya, Hiroyuki; Takagi, Tomo; Yamasaki, Izumi; Denbow, D Michael; Kangawa, Kenji; Furuse, Mitsuhiro
Animal StudyPreliminary evidence
The takeaway

Contrary to mammals, chicken ghrelin and GHRP-2 inhibited food intake in neonatal chicks, revealing a fundamental species difference in ghrelin's appetite regulation that may reflect evolutionary divergence.

Opposite effect

The same peptide (ghrelin) that stimulates appetite in mammals SUPPRESSES it in chickens — evolution reversed its function

What the researchers found

Intracerebroventricular chicken ghrelin and GHRP-2 inhibited food intake in neonatal chicks — the opposite of the appetite-stimulating effect in mammals — revealing a fundamental species difference in ghrelin signaling.

Why it matters

This species difference reveals that ghrelin's appetite function isn't universal — it evolved differently in birds. This has implications for understanding appetite regulation evolution and for extrapolating mammalian drug research across species.

How the study worked

Animal study using ICV injection of chicken ghrelin and GHRP-2 in neonatal chicks. Food intake measured following central administration compared to saline controls.

What this study cannot tell us

Neonatal chicks may respond differently from adult chickens. ICV administration bypasses normal physiological delivery. The mechanism of the reversed effect was not determined.

How to read the evidence

Preliminary animal evidence demonstrating a clear and unexpected species difference in ghrelin's appetite function.

When this study was published

Published in 2002. The avian ghrelin paradox has been confirmed and partially explained by differences in hypothalamic circuit organization.

The bigger picture

The same peptide having opposite effects in birds versus mammals reveals how evolution has repurposed ancient signaling molecules. This complicates cross-species drug testing and illuminates appetite regulation diversity.

Questions still open

  • Why did ghrelin's appetite effect reverse in birds?
  • Does this mean ghrelin has a fundamentally different brain circuit in birds?
  • Could understanding this difference reveal alternative appetite regulation pathways?

Common questions

Does ghrelin work the same in all animals?
No. In mammals, ghrelin stimulates appetite. In chickens, it suppresses appetite — the complete opposite. This shows the same peptide can have opposite effects in different species.
Why does this matter?
It means we can't assume drugs that work in mice will work the same in all species. It also reveals that appetite regulation evolved differently in birds, which could help us understand alternative weight control mechanisms.

Read the original research

Chicken ghrelin and growth hormone-releasing peptide-2 inhibit food intake of neonatal chicks.

European journal of pharmacology, 453(1), 75-9

View on PubMed ↗

Citation

Saito, Ei-suke; Kaiya, Hiroyuki; Takagi, Tomo; Yamasaki, Izumi; Denbow, D Michael; Kangawa, Kenji; Furuse, Mitsuhiro. (2002). Chicken ghrelin and growth hormone-releasing peptide-2 inhibit food intake of neonatal chicks.. European journal of pharmacology, 453(1), 75-9.