Isolation of smooth muscle excitatory substances from chicken rectum and their characterization.

Acid-acetone extracts of the chicken rectum were subjected to chromatographic and electrophoretic separation, and two new smooth muscle-contracting substances close to purity were obtained. One of them showed chemical and biological characteristics similar to those of substance P, but it was clearly different from substance P on the basis of chromatographic and electrophoretic criteria. Thus, one could be a peptide belonging to the substance P-family. The other substance was also shown to be of peptide nature since its biological activity was destroyed by chymotrypsin and carboxypeptidase A. Parallel bioassay on the two tissues of the longitudinal muscle of the guinea-pig ileum and the isolated whole chick rectum revealed that none of the peptides such as substance P, physalaemin, kassinin, eledoisin, bradykinin and angiotensin II could be a candidate for the active substance. The biological activity was not antagonized by naloxone, suggesting that the substance was a peptide other than the opioid compounds. The molecular sizes estimated by gel filtration are 1300 for the substance P-like peptide and 1600 for the other substance. The possible physiological roles of the two substances as an excitatory non-adrenergic, non-cholinergic transmitter were discussed.