Cholecystokinins in rat cerebral cortex: identification, purification and characterization by immunochemical methods.

Cholecystokinins in rat cerebral cortex were studied by radioimmunoassay using an antiserum specific for the COOH-terminus of CCK8. Total concentrations of immunoreactive CCK in cortex were 3-4 fold higher than in jejunum. Rat cerebral CCK was purified by immuno-affinity adsorption to the IgG fraction of CCK antisera conjugated to Sepharose beads, and by gel filtration and ion exchange chromatography. Over 90% of immunoreactive CCK in cortex was accounted for by a factor with the properties of synthetic CCK8, and by a closely related slightly less acidic peptide. In contrast, intestinal CCK consisted of about equal amounts of CCK8-like activity and a larger less acidic immunoreactive component. In both cortex and intestine CCK8-like activity was obtained in substantially higher yield after extracting at neutral pH in boiling water than after extracting in either 0.2 M HCl or 0.5 M acetic acid. However, the larger molecular weight forms of CCK in the intestine were recovered in similar yield by acid and neutral extraction. The principal large form of rat CCK was distinguishable from porcine CCK33 on the basis of both optimum extraction conditions and chromatographic properties. It is suggested that the different distribution of immunoreactive CCK in rat brain and gut can be explained in terms of different biosynthetic processing pathways.