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

Area of Science:

• Neuroscience
• Gastroenterology
• Biochemistry

Background:

• Cholecystokinins (CCK) are peptides found in both the brain and gut.
• Understanding CCK distribution and forms is crucial for elucidating their diverse physiological roles.

Purpose of the Study:

• To investigate the forms and concentrations of cholecystokinins in the rat cerebral cortex and jejunum.
• To compare the extraction and purification methods for CCK in these tissues.
• To explore potential differences in CCK biosynthesis between the brain and gut.

Main Methods:

• Radioimmunoassay (RIA) using a COOH-terminus specific antiserum for CCK8.
• Immuno-affinity adsorption, gel filtration, and ion exchange chromatography for CCK purification.
• Extraction at neutral pH, acidic conditions (0.2 M HCl, 0.5 M acetic acid), and boiling water.

Main Results:

• Rat cerebral cortex contains 3-4 fold higher immunoreactive CCK than the jejunum.
• Over 90% of cerebral CCK is CCK8-like, with a smaller, less acidic variant.
• Intestinal CCK comprises roughly equal amounts of CCK8-like and larger, less acidic forms.
• Neutral pH extraction in boiling water yielded higher CCK8-like activity in both tissues compared to acid extraction.
• Larger intestinal CCK forms showed similar recovery with both neutral and acid extraction.
• The principal large form of rat CCK differs from porcine CCK33.

Conclusions:

• The rat cerebral cortex primarily contains CCK8, unlike the jejunum, which has larger molecular weight forms.
• Extraction at neutral pH in boiling water is optimal for recovering CCK8-like activity.
• Differences in CCK distribution and molecular forms suggest distinct biosynthetic processing pathways in the rat brain and gut.