Forestomach motility in the chronically vagotomized sheep

Abstract

SUMMARY1. 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 05--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 jug/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 ofthe 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.

Inhibition of reticulo‐ruminal motility by volatile fatty acids and lactic acid in sheep.

“…Ruminal VFA infusion gradually reduced the amplitude and frequency of the large group discharges (Fig. 6) which are characteristic of the organized intrinsic motility of the chronically vagotomized sheep (Gregory, 1982). At high ruminal VFA concentrations all large group discharges ceased and were replaced by an increased amount ofsmall group discharges (Fig.…”

“…These animals were maintained by intragastric infusion of a complete liquid diet (Orskov et al 1979) via the rumen cannula and abomasal catheter. Nine of them were subsequently vagotomized, as previously described (Gregory, 1982) and again maintained by intragastric infusion.…”

“…Twenty-four were fitted with an abomasal catheter (polyvinyl chloride, 8 mm diameter), a rumen cannula (polypropylene, 45 mm diameter) and up to twelve sets of three nichrome-wire electrodes implanted into the wall of the reticulum and across the dorsal and ventral sacs of the rumen (Fig. 4) as previously described (Gregory, 1982). These animals were maintained by intragastric infusion of a complete liquid diet (Orskov et al 1979) via the rumen cannula and abomasal catheter.…”

“…The animals were allowed 2 weeks to recover from surgery and were housed in metabolism cages under constant lighting. Motility was recorded by electromyography and ruminal pressure via an open-ended catheter with slow continuous infusion of water on a polygraph recorder (Grass Model 7D) as previously described (Gregory, 1982) and integrated recordings were made using a polygraph integrator (Grass Model 7P lOB).…”

Contrôle nerveux de la motricité du réticulo-rumen

“…Bien que les centres gastriques reçoivent des influences provenant de centres situés au-dessus du tronc cérébral, peut-être de l'hypothalamus (Andersson, 19511, on peut conclure que le rythme et l'amplitude des contractions gastriques dépendent surtout de la mise en jeu de réflexes longs, pour la plupart vago-vagaux. Or des contractions dites intrinsèques, apparaissent en une à deux semaines après la bivagotomie (Ruckebusch, Tsiamitas et Bueno, 1972 ;Gregory, 1982) ; elles sont recueillies presque simultanément sur tout le réticulum-rumen (Gregory, 1982), ce qui montre bien qu'une région « pace-maker » supportant l'hypothèse d'une organisation périphérique de la motricité chez le mouton intact, n'existe pas. Cette motricité intrinsèque dépend de l'activation des plexus intrapariétaux au sein desquels se réalisent des réflexes courts (Gregory, 1984a (Gregory, 1984b).…”