Biological activity of two gonadotropin-releasing hormone-like peptides extracted from the cnidarian Renilla koellikeri

The family of gonadotropin-releasing hormones (GnRHs) has been considered a vertebrate preserve until recently when new members were discovered in protochordates and GnRHlike immunoreactivity (GnRH-IR) was detected in neurons and extracts from molluscs. We provide evidence that such peptides exist and are biologically active in representatives of the lowest invertebrates in which neurons are identifiable. Two GnRH-like peptides were extracted by HPLC-RIA from the sea pansy R. koellikeri and found to mimic mammalian and chicken II GnRHs in causing an inhibition of peristaltic contractions, an activity which involves the circular musculature in the sea pansy. As GnRH-IR neurons were found to innervate the circular musculature of the body wall in the sea pansy and in the starlet anemone Nematostella vectensis, we suggest that GnRH-like peptides are involved in the modulation of peristalsis in these anthozoans. Supported by NSERC of Canada.