Action of caerulein and caerulein-like peptides on "short-circuit current" and acid secretion in the isolated gastric mucosa of amphibians

Caerulein produced an increase of the short-circuit current in the isolated gastric mucosa of Rana esculenta and Bufo viridis. Threshold concentrations were of the order of 10–10 M and 3×10–11 M, respectively. A dose-response relationship was observed for concentrations of the polypeptide up to 10 to 20 times the threshold. At the same time, the polypeptide also caused an increase in the secretion of hydrochloric acid by the isolated mucosa, as measured by a direct titrimetric method. The effects of caerulein were atropine-resistant, and hence not mediated through a cholinergic mechanism. The action of caerulein on short-circuit current was compared to that of a number of synhtetic caerulein-like peptides and to that of other miscellaneous stimulants of gastric acid secretion. This study allows some conclusions to be drawn as to the relationship between chemical structure and biological activity, and largely confirms results obtained with other test preparations. With the exception of some caerulein-like peptides, no other compound could compete with caerulein in its stimulant action on the isolated amphibian gastric mucosa: cholecystokinin possessed 3% of the activity of caerulein, histamine approximately 0.1%, human gastrin I, pentagastrin and carbachol barely 0.01%.