Ontogeny of molecular forms of CCK-peptides in rat brain and gut

COOH-terminal immunoreactive cholecystokinin (iCCK) in methanol and acid extracts of brain and gut in the developing rat between 3 and 28 days after birth and in the adult has been fractionated on Sephadex G50. The single peak observed in methanol extracts of brain has an elution volume identical to that of CCK8. Acid extracts of brain contain only 10% as much iCCK as methanol extracts in a molecular form that appears to be a larger precursor because its elution volume on Sephadex is earlier than that of CCK33 or 39. Methanol extracts of duodenum at all ages contain a molecular form which is larger than CCK12 and about equal in abundance to CCK8. Acid extracts of rat duodenum contain 3 peaks: one elutes in the region of a previously described precursor form, CCK58: another co-elutes with CCK33 or 39; the third peak appears to be lower in molecular weight and is most prominent in the 2 week rat duodenum. Whether the larger iCCK found in methanol extracts or the smaller form found in acid extracts is derived from a common CCK precursor is yet to be determined.