Primary structures and effects on gastrointestinal motility of tachykinins from the rainbow trout

Purification and structural characterization of tachykinins from rainbow trout (Oncorhynchus mykiss) intestine has demonstrated the presence of three different peptides related to the mammalian tachykinins: substance P, neurokinin A, and neuropeptide-γ. The substance P- and the neurokinin A- related peptides present in the intestine are identical to the tachykinins previously isolated from the trout brain. The neuropeptide-γ-related peptide (Ser-Ser-Ala-Asn-Pro-Gln-Ile-Thr-Arg-Lys-Arg-His-Lys-Ile-Asn-Ser-Phe-Val- Gly-Leu-Met-NH₂), not previously identified in brain tissue, has the sequence of the neurokinin A-related tachykinin at its COOH-terminus. Both trout substance P and neurokinin A stimulated the motility of isolated trout intestinal muscle [pD₂ (-log of EC₅₀) values 8.5 ± 0.15 and 7.35 ± 0.08, respectively] and the vascularly perfused trout stomach (pD₂ values 9.63 ± 0.23 and 8.18 ± 0.23, respectively). Trout substance P was 14 times more potent than trout neurokinin A in the intestine and 28 times more potent in the stomach. The data suggest that receptors interacting with tachykinins in the trout gastrointestinal tract have a similar selectivity as the mammalian NK-1 receptor.