Initiation of migrating myoelectric complex in sheep by duodenal acidification and hyperosmolarity: role of vagus nerves.

Abstract

SUMMARY1. Gastrointestinal motility was studied in conscious sheep by X-radiography and by electromyography from chronically implanted electrodes before and after total thoracic vagotomy.2. Duodenal infusion of 0 5-3 mmol HCl (0*035-01 M-HCl) induced premature duodenal regular spiking activity (r.s.a.) within 1-7 min in fifteen of seventeen sheep studied when infused at 20 min after a natural r.s.a.3. There was no correlation between abomasal pH and any phase of the migrating 5. Vagotomy did not prevent the initiation or migration of the m.m.c., but reduced the rate of propagation of the r.s.a. from 40-5+7-2 (mean+S.E. of mean) to 16-7+0-1 cm/min in the duodenum, from 27-3+441 to 16-6+0 8 cm/min in the jejunum, and from 21 4 + 1 1 to 13-7 + 0 7 cm/min in the proximal ileum. Initially the frequency of r.s.a. increased, especially in the duodenum where they recurred at an interval of 98-4 + 6-8 min before vagotomy; and at 23-4 + 1P8 min in the first 24 h after vagotomy; the interval had lengthened to 86-7 + 5-2 min 2-3 weeks after vagotomy.6. Premature duodenal r.s.a. was not induced by duodenal infusion of HCl in five, or by duodenal infusion of hyperosmolar NaCl in three chronically vagotomized sheep.7. It is concluded that the vagus nerves contribute to the regulation of the frequency and propagation of the m.m.c. in sheep; duodenal acidification is not essential nor is it the normal stimulus for initiation of r.s.a., but duodenal infusion of HCl or hyperosmolar NaCl can initiate a premature duodenal r.s.a. via the vagus nerves.

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

“…Although an increase in the abomasal concentration of hydrogen ions might cause similar effects it seems unlikely that the effects presently observed were caused by hydrogen ions rather than by undissociated VFAs or lactic acid or acid anions since in the course of these experiments the abomasal pH only decreased from 3 0 to 2-8. Furthermore, in another study, abomasal pH has been shown to fluctuate widely during the day, between 2-5 and 4 0 (Gregory, Rayner & Wenham, 1984), yet such increases in reticular frequency as recorded in the present experiment have never been observed to occur naturally in this laboratory in over fifty continuous 24 h recordings of reticulo-ruminal motility.…”

Cholinergic control of pacemaker initiating phase III of the migrating myoelectric complex in sheep

“…As motilin action can be exerted directly on the smooth muscles and indirectly, through the cholinergic system, there is also evidence for the cooperation between other important mechanisms in their control of gastrointestinal motility due to the presence of cholinergic intemeurons within the enteric nervous system connected with non-adrenergic non-cholinergic (NANC) neurons (Vizi et al, 1984;Grider, 1994). The effect of such cooperation can either be stimulatory or inhibitory, which can be illustrated by the reported inconsistent effect of vagotomy on gastrointestinal motility (Gregory et al, 1984;Malbert and Ruckebusch, 1989). Thus, it can be concluded that the cholinergic system may participate directly and indirectly in the control of gastrointestinal motility, including the MMC pattern and further extensive studies are necessary to elucidate its precise role in sheep.…”

Involvement of Serotonergic Mechanisms in the Disruption of Ovine Duodenal Migrating Myoelectric Complex Cycles by Duodenal Acidification

“…This ability of duodenal acidification to elicit premature duodenal RSAs has been observed in dogs [4], cats [5], sheep [1,2] and man [3], In sheep, the vagus nerve has been reported to be involved in the media tion of these premature RSAs [1]. In man, their mediation relies on functional duode nal postganglionic cholinergic nerves [3], and in the cat, cholinergic pathways have been implicated [5], In the present investiga tion, premature RSAs induced by duodenal acidification were not blocked by 5-HT2 an tagonists, a finding which suggests the ab sence of a serotonergic pathway incorporat ing 5-HT2 receptors in the mediation of these premature RSAs.…”

“…5]. In sheep, these premature RSAs depend on the vagus nerve [1], whereas in man, they rely on duodenal postganglionic cholinergic nerves [3]. When large quantities of HC1 are used to acidify the proximal duodenum of conscious sheep, in addition to premature duodenal RSAs, a transient inhibition of reticular and abomasal motility and severe disturbances in the patterns of subsequent MMC cycles have been reported [1].…”

“…The pre mature duodenal RSA and inhibition of reticular motility also elicited by these infusions appeared to be independent of this serotonergic system. Acidification of the proximal duodenum with infusions of exogenous HC1, induces premature phases of myoelectric regular spiking activity (RSA) in the duodenum which are similar to the RSA phases (activity front, phase III) of the migrating myoelectric complex (MMC) cycle [1][2][3] and an increase in duodenal motility [4. 5].…”