Forestomach motility in the chronically vagotomized sheep

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Abstract
The motility of the reticulorumen and omasum in conscious sheep was studied by electromyography [EMG] from chronically implanted nichrome wire electrodes. The sheep were subjected to vagotomy and were maintained totally by intragastric infusion of liquid nutrients before and after vagotomy. Before vagotomy the motility of the forestomach was essentially similar to that seen in roughage-fed sheep. Bilateral thoracic vagotomy transiently abolished all electrical activity of the reticulorumen and omasum, but within 1 day some activity returned. Frequent periods of rhythmic local small group discharges were seen over the reticulorumen, while the omasum showed prolonged (1-5 min) bursts of mainly slow wave activity. Within 1-2 wk of vagotomy, strong contractions of the reticulorumen were visible by radiography. Electromyographically, they comprised a rhythmic series of some 2-5 large group discharges recurring approximately once a minute. Each series of activity was separated from the next by a short period of quiescence. The discharges occurred almost simultaneously over the whole reticulorumen and so contrasted with the progressive forward or backward spread of activity seen in the intact animal. The bursts of activity in the omasum, lasting 0.5-2 min, were not coordinated with the activity of the reticulorumen as they are in the intact animal. The activity in the reticulorumen and omasum was not affected by bilateral section of the splanchnic nerves and removal of the celiacomesenteric ganglia. Reticulorumen, but not omasal activity, was abolished by atropine (0.1 mg/kg) or hexamethonium (2 mg/kg), while both were stimulated by pentagastrin (3 .mu.g/kg). Following vagotomy reticulorumen motility was no longer influenced by feeding or by tactile stimulation of the buccal cavity or esophagus. Severe distension of the abomasum caused a slight acceleration of the motility rhythm compared to the inhibition seen before vagotomy. The reticulorumen motility observed after vagotomy is an intrinsic cholinergic motility which is dependent upon the activity of the myenteric plexus. The motility of the omasum after vagotomy is similar to that seen in the intact animal and differs from that of the rumen in that it appears not to depend wholly upon cholinergic control.