Isolation of a Peptide Material Showing Strong Rectal Muscle-Contracting Activity from Chicken Rectum and Its Identification as Chicken Neurotensin

Abstract

A peptide with strong activity to contract isolated whole chick rectum, RC-substance, in an acid-acetone extract prepared from 2.0 kg wet weight of chicken rectums was isolated by gel filtration on Sephadex G-25, ion exchange chromatography on a SP-Sephadex C-25 column, and high voltage paper chromatography. The close purity of this substance was established by high performance liquid chromatography (HPLC). The RC-substance displayed the same pharmacological and enzymatic properties as bovine neurotensin (NT). However, it differed from bovine NT in its behavior during the ion exchange chromatography, in its mobility during the electrophoresis, and in its retention time on HPLC. The amino acid analysis by a conventional OPA method revealed that all ten amino acid residues of which molar ratios were integral were common with those of chicken NT. Its biological activities were equipotent to those of bovine NT, suggesting the presence of proline in the COOH-terminal hexapeptide. From these results, it can be concluded that the RC-substance is identical to chicken NT. Exposure to high concentrations of bovine NT rendered the rectal smooth muscle of the chicken insensitive to subsequent applications of the RC-substance as well as bovine NT. This desensitization also reduced specifically the contractile responses of the rectal muscle elicited by non-adrenergic and non-cholinergic (NANC) nerve stimulation, suggesting a possible physiological role of the RC-substance as the neurotransmitter of NANC neurones.