INTERACTION BETWEEN CCK AND OPIOIDS IN THE MODULATION OF THE RECTOCOLONIC INHIBITORY REFLEX IN RATS

The effects of cholecystokinin octapeptide (CCK-8) as well as the invo lvement of opioid system were evaluated in rectal distension (RD)-indu ced colonic motor inhibition in rats. Rats were surgically prepared wi th electrodes implanted on the proximal colon, and a catheter was impl anted in lateral ventricle of the brain. RD was performed by inflation (0.0-1.6 mi) of a balloon rectally inserted. RD 1.6 ml of induced an inhibition of the colonic spike bursts (3.1 +/- 0.5 per 5 min vs. 8.1 +/- 0.4 before RD). Intracerebroventricular but not intravenous inject ion of CCK-8 and A-71623 (50 and 100 ng/kg) reduced the RD-induced col onic motor inhibition, whereas A-63387 was ineffective. PD-135,158 (10 mu g/kg icv) suppressed the inhibitory reflex caused by RD. Devazepid e (100 mu g/kg icv) had no effect in this reflex function. Devazepide (1 mu g/kg), naloxone (0.1 mg/kg), and nor-binaltorphimine (nor-BNI; 1 0 mg/kg) reversed the blocking effect of CCK-8, whereas PD-135,158 (0. 1 mu g/kg) and naltrindole (1 mg/kg) have no effect. In conclusion, CC K-8 acts on central alimentary cholecystokinin receptors to modulate t he RD-induced inhibition of colonic motility through pathways involvin g activation of endogenous kappa-receptors.