naloxone and cholecystokinin-39

The effects of cholecystokinin (CCK) and gastrin on proximal and distal colonic motility were investigated because of the possible role of these peptides in feeding-induced colonic motility. Experiments were performed using 22 chloralose-urethane anaesthetized cats in which the colon was acutely denervated. The volume changes of the proximal and distal colon were recorded with water-filled flaccid balloons. The venous effluxes from the proximal and distal colon were recorded separately using drop recorder units. CCK-8, I-200 pmol X min-I close i.a., and pentagastrin, I-200 pmol X min-I close i.a., evoked dose-dependent contractions of the colon without altering systemic arterial blood pressure and colonic blood flow. The CCK peptides -8, -33 and -39 produced contractions of similar magnitude in the proximal and distal colon. The stimulatory effect of CCK-8 and pentagastrin on colonic motility was blocked by tetrodotoxin (I microgram X kg-I i.a.) and hexamethonium (I0 mg X kg-I i.v.). Atropine (0.5 mg X kg-I i.v.) completely blocked the responses to CCK-8 and pentagastrin in the distal colon but only partially in the proximal colon. Additional administration of naloxone (I mg X kg-I i.a.) abolished the remaining contractile response to the peptides in the proximal colon. The present results support the idea that CCK and pentagastrin have a stimulatory effect on distal colonic motility mediated via preganglionic and postganglionic cholinergic pathways. The possible role of opioid peptides and cholinergic mechanisms in the proximal colon is discussed.

Topics: Animals; Atropine; Cats; Cholecystokinin; Colon; Dose-Response Relationship, Drug; Female; Gastrointestinal Motility; Infusions, Intra-Arterial; Male; Naloxone; Pentagastrin; Peptide Fragments; Regional Blood Flow; Tetragastrin