Distribution and molecular heterogeneity of cholecystokinin-like immunoreactive peptides in the brain and gut of the rainbow trout, Salmo gairdneri.

Cholecystokinin-like immunoreactivity (CCK-li) was measured in extracts of various brain and gut regions of the rainbow trout, Salmo gairdneri. All regions of the brain except the cerebellum and pituitary contained detectable CCK-li. In the gut, the highest concentrations of CCK-li were found in the small intestine and pyloric caeca. Lesser amounts were found in rectum and gastric antrum extracts. In some fish, extracts of these regions contained no detectable CCK-li. Rainbow trout brain extracts contained CCK-li that co-eluted with CCK-8 in gel permeation chromatography whereas CCK-li extracted from the various gut regions exhibited marked molecular heterogeneity. Tissue distribution and apparent molecular size of CCK-li in trout is very similar to mammals for brain but distinct from the mammalian pattern in the gut.