Ileal expression of gastrin and cholecystokinin

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Abstract
Antibodies against the common active site of cholecystokinin (CCK) and gastrin stain three endocrine celltypes in the gut: G-cells (that synthesize gastrin) I-cells (that synthesize CCK), and TG-cells (whose product 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 TGthan G- and I-cells. Ileal CCK and gastrin mRNA corresponded to those of the antroduodenal mucosa. Gel, ion-exchange and reversed-phase chromatography monitored with sequence-specific immunoassays showed that the ileal mucosa on average contain 0.3 and 7.6 pmolg progastrin and proCCK, respectively; 1.1 and 13.5 pmolg glycine-extended intermediates; and 1.1 and 24.8 pmolg of bioactive carboxyamidated gastrin and CCK, respectively. Gastrin was present only as non-sulfated gastrin-34, whereas CCK occurred in forms similar to those of the proximal intestine. Although ileal progastrin processing is tissue specific, the amounts of gastrin and CCK are too small to explain the TG-cells. Moreover, since the ileal extracts were without traces of other peptides having the C-terminus common to gastrin and CCK, the results suggest that TG-cells produce a peptide, which is only weakly related to gastrin and CCK