Concentration and in vivo synthesis of cholecystokinin in subcortical regions of the rat brain

The in vivo biosynthesis of cholecystokinin (CCK) in subcortical regions of the rat brain was studied by intracisternal pulse injections of [35S]methionine. The rats were killed 1.0 or 1.5 h after the injection. Subcortical CCK extracted in boiling water and acetic acid was immunoabsorbed by an antiserum specific for the COOH-terminal sequence of CCK. Gel chromatography of the absorbed CCK separated four molecular forms with elution constants (Kav) of 0.08, 0.50 (corresponding to the tritriacontapeptide amide, CCK-33), 1.10 (corresponding to the COOH-terminal octapeptide, CCK-8), and 1.40 (a component which may correspond to the COOH-terminal tetrapeptide amide). Significant incorporation of [35S]methionine occurred in the largest (Kav approximately 0.08) and octapeptide-like form only. Chasing with methionine indicated a precursor relationship between the largest form and CCK-8. The results demonstrate a substantial synthesis of CCK also in subcortical regions of the brain.