Presence of a substance P‐like peptide in an acid extract of the intestinal bulb of the carp (Cyprinus carpio)

Abstract

The effect of an acid extract of the carp intestinal bulb (ECI) on guinea‐pig ileum longitudinal smooth muscle (GPLM) and carp intestinal bulb longitudinal smooth muscle (CIBLM) was examined. ECI caused a concentration‐dependent contraction of GPLM and CIBLM. This ECI‐induced response was reduced by atropine to 30–40% of the control, indicating that part of the contracting activity of ECI is attributable to acetylcholine. The atropine‐resistant contracting activity of ECI was not mediated by histamine, 5‐hydroxytryptamine, ATP, ADP, angiotensin II, neurotensin, vasoactive intestinal peptide or an opioid peptide. The active material mediating the atropine‐resistant contracting activity is probably a peptide, because the contraction in response to ECI was abolished on incubation with pepsin or α‐chymotrypsin. [D‐Pro2, D‐Trp7,9]‐substance P, [D‐Pro4, D‐Trp7,9]‐substance P (4–11) decreased the atropine‐resistant contracting activity of ECI as did desensitization induced by substance P. On a Sephadex G 25 column, the active material was eluted as one peak. The active fractions were pooled and then applied to another Sephadex G25 column to compare the Ve/Vo value for the active material with those for peptides of known molecular weights. The molecular weight of the active material was estimated to be 1200–1700 (1410 ±70, n = 6). The results indicate the presence of a substance P‐like peptide in the carp intestinal bulb. 1988 British Pharmacological Society