Radioimmunoassay for the tachykinin peptide physalaemin: Detection of a physalaemin-like substance in rabbit stomach

Abstract

An antiserum against the amphibian tachykinin physalaemin was specific for the NH₂-terminal region of this peptide. The cross-reactivity of antiserum PS-1 with uperolein was 2.03%, phyllomedusin, 0.36%, and kassinin, 0.013%; negligible (<0.0001%) recognition was shown for substance P as well as with numerous other polypeptide hormones. The assay readily detected 1 pg (0.79 fmol) physalaemin with 50% displacement at 6.79 ± 1.98 pg (5.29 ± 1.54 fmol). Rabbit stomach, extracted by boiling followed by homogenization in 1.0 n formic acid, contained physalaemin-like immunoreactivity. The concentration detected in the antrum was 43.0 ± 7.3 ng/g dry weight with less in the fundus, pylorus, corpus, and duodenum. Chromatography of the extracts on Bio-Gel P4 columns in 0.1 n formic acid gave a single, symmetrical peak of immunoreactivity which eluted with an apparent molecular weight of approximately 1700. These data are the first to demonstrate the presence of a peptide with physalaemin-like immunoreactivity in mammalian tissues.