In vitro response of rat gastrointestinal segments to cholecystokinin and bombesin

In previous studies of the rat gastrointestinal (GI) tract, we have demonstrated specific binding of cholecystokinin (CCK) to the pylorus and of bombesin (BN) to the gastric fundus, gastric antrum, duodenum, and ileum. We now present the results of an investigation of the in vitro response of the same regions of the rat GI tract to CCK-8 (the active octapeptide of CCK) and BN. Sections of rat fundus, antrum, pylorus, duodenum, and ileum were suspended in a Tyrode buffer and attached to an isometric pressure transducer in a longitudinal orientation. Dose-response curves to CCK-8 and BN were generated for each tissue. CCK-8 consistently induced a change only in pylorus, while BN induced a response from fundus, antrum and duodenum. With the exception of the lack of ileal response to BN, the regions of the rat GI tract which biologically respond (i.e., contract or relax) to CCK-8 or BN were the same regions in which we have located BN and CCK-8 binding sites. This correlation supports the hypothesis that GI function is modified by specified hormone-receptor interactions with these peptides.