Antagonistic effects of naloxone on CCK-octapeptide induced satiety and rumino-reticular hypomotility in sheep

Abstract

Continuous intracerebroventricular (ICV) infusion of CCK-octapeptide (CCK 8) was performed in ewes fitted with a permanent cannula into the lateral cerebral ventricle and Nichrome electrodes on the reticulum in order to record its electrical activity. In the first series of experiments, subsequently repeated in 12 h fasted animals, CCK 8 was infused during the first hour of a 3 hour period of feeding at 2.5, 5 and 10 ng.kg −1 .min −1. The same series of infusion were performed 20 min after ICV injection of 2.4 and 10 μg.kg −1 of naloxone. CCK 8 reduced significantly in a dose related manner the food intake (r = 0.95; P < 0.01) and the frequency of cyclic spike bursts associated to biphasic contractions of the reticulum observed during feeding (r = 0.89 ; P < 0.01). At 5 and 10 ng.kg −1 .min −1, the reduction of food intake reached 46.2 and 52.6 % during the period of infusion ; the basal and stimulated (feeding) frequency of reticular contractions were nearly halved. Previous ICV administration of naloxone (2.4 μg.kg −1) partially blocked the effects of CCK 8 infusion on both food intake (72 %) and reticular frequency (54 % basal, 67 % stimulated). The CCK 8 induced effects on both food intake and frequency of reticular contraction were completely abolished after a previous 10 μg.kg −1 injection of naloxone. These results suggest that the central effects of CCK 8 on feeding behavior and forestomach motility involve similar central structures and are mediated through opiate receptor structures.