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Cholecystokinin (CCK) appears to induce profound alterations in intestinal motility but in ruminants the question has not been entirely explored. Thus this study aimed to examine the precise effects of CCK-octapeptide (CCK-OP) and its amphibian analogue, cerulein, on duodenal motor activity in non-fasted rams in chronic experiments. Six adult rams underwent implantation of a strain gauge force transducer to the duodenal wall, and - additionally - the bipolar platinum electrodes to the duodenal bulb, distal duodenum, just near the strain gauge force transducer, and to the proximal jejunum. During ongoing motor recordings, 0.15 M NaCl or CCK peptides were administered intravenously. Slow injections of CCK-OP at doses of 20 (over 30 s), 200 (over 30 or 60 s), and 2000 (over 30, 60, or 120 s) ng/kg of body weight and slow injections of cerulein at doses 1, 10, or 100 ng/kg (given over the same periods) were each performed in the course of duodenal phases 1, 2a, or 2b of the migrating motor complex (MMC), i.e. 5 min after the onset of each phase. At least two lower doses, comparing with other studies, appeared to remain at the physiological level. Injections of the smallest doses of CCK peptides exerted a slight and mostly insignificant effect on the duodenal area under contraction (AUC). In the duodenum, the moderate doses of the hormones evoked short stimulatory followed by longer inhibitory biphasic effects on AUC. These effects were inversely related to the duration of hormone injection. It is concluded that CCK peptides may evoke stimulatory and inhibitory (biphasic) effects on duodenal motility in sheep. The observed effects of CCK-OP appear to be physiological. [ABSTRACT FROM AUTHOR]