ILEAL EXPRESSION OF GASTRIN AND CHOLECYSTOKININ - IN SEARCH OF A RELATED HORMONE

Antibodies against the common active site of cholecystokinin (CCK) and gastrin stain three endocrine celltypes in the gut: G-cells (that syn thesize gastrin) I-cells (that synthesize CCK), and TG-cells (whose pr oduct is unknown). In order to examine whether TG-cells either process progastrin or proCCK in a specific manner, or express a novel gastrin -CCK related hormone, we studied the distal porcine ileum, which have far more TG- than G- and I-cells. Ileal CCK and gastrin mRNA correspon ded to those of the antroduodenal mucosa. Gel, ion-exchange and revers ed-phase chromatography monitored with sequence-specific immunoassays showed that the ileal mucosa on average contain 0.3 and 7.6 pmol/g pro gastrin and proCCK, respectively; 1.1 and 13.5 pmol/g glycine-extended intermediates; and 1.1 and 24.8 pmol/g of bioactive carboxyamidated g astrin and CCK, respectively. Gastrin was present only as non-sulfated gastrin-34, whereas CCK occurred in forms similar to those of the pro ximal intestine. Although ileal progastrin processing is tissue specif ic, the amounts of gastrin and CCK are too small to explain the TG-cel ls. Moreover, since the ileal extracts were without traces of other pe ptides having the C-terminus common to gastrin and CCK, the results su ggest that TG-cells produce a peptide, which is only weakly related to gastrin and CCK.