Holostean fish have met-enkephalin and leu-enkephalin in a 3:1 ratio plus a novel modified form in their pituitary — but no prodynorphin-derived peptides.
No prodynorphin in ancient fishSuggesting the dynorphin system evolved after the enkephalin system
What the researchers found
Holostean fish have enkephalin peptides with a 3:1 met-to-leu ratio and a novel modified met-enkephalin form, but no detectable prodynorphin-derived peptides.
Why it matters
This suggests the enkephalin and dynorphin opioid systems may have evolved at different times. The enkephalin system appears more ancient, present even in primitive fish.
How the study worked
Pituitary and brain extracts were analyzed by immunohistochemistry, reverse phase HPLC with radioimmunoassay, and enzymatic digestion to detect extended forms.
What this study cannot tell us
This was an animal study in a single fish species. The antisera used were designed for mammalian peptides and might not detect all fish opioid variants. Absence of detection does not prove absence.
How to read the evidence
Preliminary — comparative biochemistry in a single ancient fish species.
When this study was published
Published in 1989 — contributed to understanding opioid system evolution.
The bigger picture
The absence of dynorphin peptides in ancient fish suggests the prodynorphin system evolved later. Studying primitive species reveals how the opioid peptide families diversified over evolution.
Questions still open
- When did the dynorphin system evolve?
- Is the novel fish enkephalin form biologically active?
Common questions
Why study opioid peptides in fish?
What is a holostean fish?
Read the original research
Detection of Met-enkephalin and Leu-enkephalin in the posterior pituitary of the holostean fish, Amia calva.
Peptides, 10(5), 951-6
Citation
Dores, R M; McDonald, L K; Crim, J W. (1989). Detection of Met-enkephalin and Leu-enkephalin in the posterior pituitary of the holostean fish, Amia calva.. Peptides, 10(5), 951-6.