Two novel tachykinin-related neuropeptides in the echiuroid worm, Urechis unicinctus.

Two novel neuropeptides, urechistachykinin I (H-Leu-Arg-Gln-Ser-Gln-Phe-Val-Gly-Ser-Arg-NH2) and urechistachykinin II (H-Ala-Ala-Gly-Met-Gly-Phe-Phe-Gly-Ala-Arg-NH2), were isolated from the ventral nerve cords of the echiuroid worm, Urechis unicinctus. These peptides showed a contractile action on the inner circular body-wall muscle of the animal. Their amino acid sequences were found to be significantly homologous with those of the vertebrate and insect tachykinins. The urechistachykinins potentiated spontaneous rhythmic contractions of the cockroach hindgut.