Regional differences in the effects of various doses of cerulein upon the small-intestinal migrating motor complex in fasted and non-fasted sheep

Analysis of the excitatory motor response evoked by nicotinic and muscarinic blockade of ovine small bowel

It has been reported that the administration of anticholinergic drugs evokes inhibitory and excitatory responses, but the precise character of the latter has not yet been defined. This study was thus devoted to analyzing its occurrence following various doses of hexamethonium (Hx) and atropine (At) administration in the course of different phases of the small-intestinal migrating motor complex (MMC) in fasted and non-fasted sheep and to further characterize the excitatory responses in comparison with individual phases of the MMC. Two basic types of excitatory response were found. In the course of chronic experiments, various doses of Hx and At evoked rebound excitation (RE, i.e., irregular contractions or spike bursts evoked in response to the anticholinergic drug) alternating with phase 3-like activity (not the organized phase 3 of the MMC or its parts). The intensity of these changes varied and was related to the drug dose. Thus intense and non-intense RE activity were distinguished. In non-fasted sheep, these alterations were slightly less pronounced than in fasted animals. When the drug was given during phase 1 of the MMC, RE did not occur or was greatly reduced and its arrival was delayed. Hx triggered RE mostly in the duodenum, while the action of At was most effective in the jejunum. It is concluded that Hx and At initially hamper small-intestinal motility and just after that evoke a secondary stimulatory response, i.e., phase 3-like activity and RE of different intensity, duration, and repeatability in fasted and non-fasted sheep. These stimulatory effects may resemble unorganized phases of the MMC.

Dose-related effects of cholecystokinin octapeptide administered during various phases of the migrating motor complex on small-intestinal motility in sheep

Cholecystokinin (CCK) may affect intestinal motility, but in ruminants its precise effects have not been entirely explored. The aim of this study was to examine the effects of CCK-octapeptide (CCK-OP) on small-intestinal myoelectric activity in rams in the course of chronic experiments. Five rams underwent implantation of bipolar platinum electrodes to the duodenal bulb, distal duodenum, and jejunum as well as a strain gauge force transducer attached near the duodenal electrode. During continuous myoelectric recordings, 0.15 M NaCl or CCK-OP were injected slowly into the jugular vein. 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 were each administered 5 or 30-40 min after the onset of the duodenal phase 1 or phase 2 of the migrating myoelectric complex (MMC), respectively. Most of these CCK doses were considered physiological. Injections of the smallest dose of CCK-OP exerted a slight and mostly insignificant inhibitory effect on the duodenal bulb and the duodenal myoelectric activity index (MAI) values. In the duodenal bulb, the effects of CCK-OP on myoelectric activity were dose dependent and closely related to the phase of the MMC. In the duodenum, the high dose of the hormone evoked short stimulatory and longer inhibitory biphasic effects on the MAI. These effects were inversely related to the duration of the hormone injection. It is concluded that CCK evokes a physiological stimulatory and inhibitory (biphasic) effect on the duodenal bulb and duodenal motility in sheep, with the inhibitory effect of the hormone being more pronounced in the duodenal bulb than in the duodenum. These effects were related to the CCK dose and the MMC phase. Therefore, CCK is an important regulator of upper small bowel motility in sheep.