Immunochemical studies on cholecystokinin. II. Distribution and molecular heterogeneity in the central nervous system and small intestine of man and hog.

Using sequence-specific radioimmunoassays, the distribution and heterogeneity of cholecystokinin (CCK) has been determined in extracts of tissues from the central nervous system and small intestine of adult man and hog. The CCK determinations were correlated with measurements with a radioimmunoassay specific for the structurally related peptide hormone gastrin. The amount and molecular forms of CCK extracted from brain as well as gut tissue were pHdependent in that boiling at neutral pH released mainly small molecular forms, whereas acid released mainly large forms. Consequently, the tissue was first boiled at pH 6.6, after which acetic acid was added to pH 2.5. Large amounts of CCK were found in the central nervous system with a differential distribution: cerebral cortex, 200 to 2300 pmol/g with the highest concentrations in the neocortical regions; corpus striatum, 158 to 480 pmol/g; thalamus, 8 to 59 pmol/ g; hypothalamus, 24 to 220 pmol/g; mesencephalon, 13 to 93 pmol/g, and brain stem, 6 to 43 pmol/g. In the pineal body, the pituitary gland, cerebellum, pons, and spinal cord CCK was undetectable. In contrast with CCK proper, gastrins were measured in the pituitary gland (7 to 51 pmol/g), but gastrin was not detectable in other regions of the central nervous system of the two species. Immunoreactive CCK in the brain was found by gel chromatography to be present almost exclusively in three molecular forms: 1) a minor fraction corresponding to the triacontatriapeptide, CCK,, (5%); 2) a large fraction corresponding to the COOH-terminal octapeptide of CCK,, (80%); and 3) a small immunoreactive component corresponding to the COOH-terminal tetrapeptide of CCK,,. Determination of the true concentrations of the latter peptide, however, awaits purification and use of a proper standard. Duodenum and jejunum in both species contained CCK in concentrations similar’ to those measured in the cerebral cortex, varying from 550 to 2400 pmol/g of intestinal wall. The molecular heterogeneity of intestinal CCK was similar in both species studied. CCK in gut extracts eluted in five positions on gel chromatography: 1) immunoreactivity corresponding to peptides larger than CCK,, and CCK,,, was eluted with a constant, K,, , of 0.15 to 0.20 (10% of the immunoreactivity); 2) molecular forms