Effect of the C‐Terminal Octapeptide of Cholecystokinin on Guinea Pig Ileum and Gall‐Bladder in vitro

The C‐terminal octapeptide of cholecystokinin shares the pharmacological properties of the original molecule. Both seem to act directly on the smooth muscle cell of the gall‐bladder but indirectly via a nervous pathway in the ileum. Both reduce the resistance of the choledocho‐duodenal junction. This pharmacological profile is characteristic for a group of substances which besides cholecystokinin and its C‐terminal octapeptide also includes gastrin, pentagastrin and caerulein. There is a close chemical relationship between these substances, e.g . they all have the same C‐terminal tetrapeptide. Effective doses for the octapeptide were 0.1–0.5 ng/ml in vitro . Its molar activity in the gall‐bladder and ileum is comparable to that of caerulein and about 3 times that of cholecysto kinin and 1000 times that of pentagastrin. Besides the heterologous caerulein the C‐terminal octapeptide of cholecystokinin appears as the most active gall‐bladder contracting agent known at present, with a molar activity about 100 times that of acetylcholine, histamine or bradykinin.