Amphibian Neurotensin (NT) is not Xenopsin (XP): Dual Presence of NT-Like and XP-Like Peptides in Various Amphibia*

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Abstract
To clarify whether xenopsin (XP) is the amphibian counterpart of mammalian neurotensin (NT), extracts of skin, brain, and intestine from representative amphibians were subjected to immunochemical, chromatographic, and biological analyses. The results indicated the dual presence of NT- and XP-like peptides in extracts of tissues from Xenopus laevis, Rana catesbeiana, Rana pipiens, Bufo marinus, Bufo americanus, and Necturus maculosus, which were separated during gel chromatography on Sephadex G-25 and high pressure liquid chromatography on μ-Bondapak C-18. Immunochemical studies, employing three different region-specific antisera toward NT (ox and man) and one antiserum towards XP (Xenopus laevis), indicated that the NT-like peptides shared COOH-terminal homologies with NT and differed at their NH2-termini. Two classes of NT-like peptides could be distinguished on the basis of their distributions in tissues and their cross-reactivities with the antisera; immunoreactive NT measured using antiserum HC-8 tended to be found primarily in brain and intestine, whereas that reactive with antiserum PGL-4 was most concentrated in stomach, liver, and pancreas. Although also present in brain and intestine, immunoreactive XP was highest in stomach, pancreas, and skin. Partially purified immunoreactive NT and XP obtained from gastrointestinal tissues of Xenopus laevis and Bufo marinus were shown to increase the hematocrit and induce cyanosis in anesthesized rats. These findings indicate the presence of both NT- and XP-like peptides in neural and gastrointestinal tissues from several amphibia and suggest the possibility that XP-like peptides (apart from NT) may exist in other animals.