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-gamma. 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-gamma-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.