Growth Hormone Secretagogues Act Directly on Brain Neurons in the Appetite Center | Research

The takeaway

Both GHRP-6 and non-peptide GH secretagogues activated neurons in the arcuate nucleus, confirming they work directly on brain circuits beyond just the pituitary.

Central brain action confirmed
GH secretagogues activated arcuate nucleus neurons directly — not just pituitary release, but brain circuit activation

What the researchers found

Both GHRP-6 and non-peptide GH secretagogues activated Fos expression in the arcuate nucleus and excited arcuate neuroendocrine neurons, confirming central brain actions.

Why it matters

Knowing that GH secretagogues act on specific brain regions helps explain their effects beyond just growth hormone release, including appetite stimulation and sleep effects.

How the study worked

Rats received i.c.v. or i.v. injections of GHRP-6 or non-peptide GH secretagogues. Brain Fos expression was mapped by immunohistochemistry. Arcuate neuron electrophysiology was recorded in vivo.

What this study cannot tell us

Animal study in rats. Fos expression shows activation but does not reveal the full functional significance. Brain activation patterns in rats may differ from humans.

How to read the evidence

Moderate — animal study with both anatomical (Fos) and electrophysiological evidence. Two complementary methods strengthen the finding.

When this study was published

Published in 1995 (31 years ago). The arcuate nucleus is now known to contain the ghrelin receptors that GH secretagogues target.

The bigger picture

This explains why GH secretagogues like MK-677 increase appetite — they act on the same brain region that controls hunger. Understanding these central effects helps predict and manage side effects.

Questions still open

Could the appetite-stimulating effect be separated from the GH-releasing effect?
Are the arcuate neurons the ghrelin receptor-expressing cells?

Common questions

Why do GH secretagogues increase appetite?

They act on the arcuate nucleus — the brain's appetite control center — not just the pituitary. This activates hunger-promoting neurons alongside GH-releasing ones.

Can the hunger effect be avoided?

Current GH secretagogues like MK-677 consistently increase appetite because the GH and appetite effects come from the same receptor. Separating them would require a fundamentally different drug design approach.

Read the original research

Central actions of peptide and non-peptide growth hormone secretagogues in the rat.

Neuroendocrinology, 61(1), 36-43

View on PubMed ↗

Citation

Dickson, S L; Leng, G; Dyball, R E; Smith, R G. (1995). Central actions of peptide and non-peptide growth hormone secretagogues in the rat.. Neuroendocrinology, 61(1), 36-43.