Forestomach motility in the chronically vagotomized sheep

Abstract

1. The motility of the reticulo‐rumen and omasum in conscious sheep was studied by electromyography 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. 2. Bilateral thoracic vagotomy transiently abolished all electrical activity of the reticulo‐rumen and omasum, but within 1 day some activity returned. Frequent periods of rhythmic local small group discharges were seen over the reticulo‐rumen, while the omasum showed prolonged (1‐5 min) bursts of mainly slow wave activity. 3. Within 1‐2 weeks of vagotomy strong contractions of the reticulo‐rumen were visible by radiography. Electromyographically, they comprised a rhythmic series of some two to five 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 reticulo‐rumen 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 co‐ordinated with the activity of the reticulo‐rumen as they are in the intact animal. 4. The activity in the reticulo‐rumen and omasum was not affected by bilateral section of the splanchnic nerves and removal of the coeliaco‐mesenteric ganglia. Reticulo‐rumen but not omasal activity was abolished by atropine (0·1 mg/kg) or hexamethonium (2 mg/kg), while both were stimulated by pentagastrin (3 μg/kg). 5. Following vagotomy reticulo‐rumen motility was no longer influenced by feeding, or by tactile stimulation of the buccal cavity or oesophagus. Severe distension of the abomasum caused a slight acceleration of the motility rhythm compared to the inhibition seen before vagotomy. 6. It is concluded that the reticulo‐rumen 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. © 1982 The Physiological Society