A neuropeptide in mammalian tissues with physalaemin-like immunoreactivity.

Erspamer et al. isolated several structurally related non-mammalian peptides, termed tachykinins, with biological activities similar to substance P (refs 2, 3). This similarity is due to a common COOH-terminal region, whereas the specific action of each member of the group depends on its unique NH2-terminal sequence. Based on these properties, parallel bioassays using numerous smooth muscle preparations and physiological parameters allow them to be generally distinguished. However bioassays are time consuming and not highly specific. Thus, we developed a rapid physalaemin-specific radioimmunoassay that led to the initial discovery of a substance in mammalian tissues with an immunoreactivity resembling that of the original amphibian peptide. We now present data on the distribution, localization and partial characterization of physalaemin-like immunoreactivity (PSLI) in tissues of several mammalian species.