Comparison of gastrointestinal responses to CCK-8 and associated with vomiting

The gastrointestinal motor and myoelectric responses associated with vomiting induced by apomorphine (APO) and activated by cholecystokinin octapeptide (CCK-8) were compared as well as the mechanisms of initiation of these responses. Twelve dogs were surgically implanted with strain-gauge force transducers or bipolar electrodes for chronic recording of contractile or electrical activity. The responses to CCK-8 were determined in the fasted state and compared with the gastrointestinal motor and myoelectric correlates of vomiting activated by APO. After recording control responses, the effects of the following agents on these responses were determined: atropine, domperidone, and proglumide. In addition, the effects of supradiaphragmatic vagotomy or splanchnicectomy were determined. We found that CCK-8 activated contractile and myoelectric responses in the absence of vomiting, which were similar in most respects to those found in association with vomiting. These responses included 1) the retrograde giant contraction (RGC) and 2) the post-RGC phasic contractions. These RGCs were similar with respect to their activation in an all-or-none fashion, magnitude, duration, and position in the small intestine. The myoelectric correlates of these motor responses were similar qualitatively and quantitatively. The responses activated by APO and CCK-8 differed with respect to their coordination at different levels of the gastrointestinal tract. Whether activated by CCK-8 or APO, atropine blocked the RGC but not the post-RGC contractions. Domperidone blocked all responses to APO but not to CCK-8, and splanchnicectomy did not affect responses to either agent. Vagotomy blocked all gastrointestinal responses to APO but not to CCK-8. These results indicated that CCK-8 activates the gastrointestinal motor and myoelectric correlates of vomiting by a peripheral mechanism that does not include dopamine receptors.