Gastrin/CCK-like immunoreactivity in endocrine cells and nerves in the gastrointestinal tract of the cod, Gadus morhua, and the effect of peptides of the gastrin/CCK family on cod gastrointestinal smooth muscle

Abstract

Immunohistochemistry shows the presence of one or several gastrin/cholecystokinin (CCK)-like peptides in the gastrointestinal tract of the Atlantic cod, Gadus morhua. Immunoreactive (IR) endocrine cells are present mainly in the lower part of the cardiac and in the pyloric stomach, with a concentration to the inner curvature, and in the proximal part of the intestine, especially in the area of the pyloric caeca, after which the population density of IR cells decreases anally. IR nerve fibers are found in the myenteric plexus and muscle layers of the stomach only. Radioimmunoassays, performed with two C-terminal specific gastrin/CCK antisera, confirm the immunohistochemical findings. The highest levels of IR material are found in the mucosa of the pyloric caeca, the proximal intestine, and the pyloric part of the stomach. The smooth muscle layers contain IR material in decreasing gradient toward the rectum. The excitatory effect of gastrin/CCK-related peptides on gut smooth muscle is investigated in isolated strip preparations of the gut wall. Of the peptides tested, cerulein is the most potent, followed by CCK 8.and gastrin 17, while gastrin 5 is the least effective. Sulphated CCK 8 gives a higher amplitude of the response but in the same concentration range as nonsulphated CCK 8. It is concluded that one or several gastrin/CCK-like peptides are present in the gut of the cod and may be involved in the nervous and endocrine control of the cod gut motility.