Effects of 5-Hydroxytryptamine Agonists on Myoelectric Activity of the Forestomach and Antroduodenal Area in Sheep

Abstract

To increase knowledge of the role of 5-hydroxytryptamine (5-HT) receptors in the regulation of reticuloruminal, omasal and antroduodenal myoelectric activity in sheep, the effects of 5-HT agonists on forestomach and antroduodenal myoelectric activity have been investigated in conscious sheep. 5-Carboxamidotryptamine, methysergide, alpha-methyl-5-HT, 2-methyl-5-HT, cisapride, zacopride or metoclopramide were infused intravenously for 5 min and myoelectric recordings were obtained from electrodes chronically implanted in the reticulum, rumen (dorsal sac), omasal body, abomasal antrum and duodenal bulb. The integrated activity of the reticular and ruminal spike bursts was modified only by the highest doses of alpha-methyl-5-HT, 2-methyl-5-HT, metoclopramide and cisapride. A phase III-like activity pattern was recorded in the antroduodenal area with all 5-HT-ergic agents and a dose-dependent inhibition of myoelectric activity was recorded in both reticulorumen and omasum at the same time as the antroduodenal effects. In the forestomach, methysergide alone induced inhibition of ruminal secondary contractions; 5-HT, alpha-methyl-5-HT, cisapride and metoclopramide, moreover, evoked an initial dose-dependent increase in antral activity. These results suggest that 5-HT1, 5-HT2, 5-HT3 and 5-HT4 receptors are involved in the regulation of the migrating myoelectric complex in sheep and in the genesis of forestomach hypomotility that is occasionally recorded concomitantly with the spontaneous duodenal phase III in sheep. 5-HT4 receptors also have a prokinetic action in the antral area.

Modification of spontaneous contractility of smooth muscle preparations from the bovine abomasal antrum by serotonin receptor agonists

“…, 2000). In an electromyographical study on conscious sheep (Plaza et al. , 1996), α ‐M‐5‐HT evoked a dose dependent increase in antral activity and a dose‐dependent inhibition of the myoelectrical activity of both the reticulorumen and the omasum.…”

“…, 1994). The effects of 5‐HT agonists on myoelectric activity of the forestomach and antroduodenal area were investigated (Plaza et al. , 1996).…”

Quantitative mRNA Analysis of Eight Bovine 5‐HT Receptor Subtypes in Brain, Abomasum, and Intestine by Real‐Time RT‐PCR

“…In another study in sheep, 5-HTR 1A , 5-HTR 2 , 5-HTR 3 , and 5-HTR 4 are reported to be involved in the regulation of forestomach motility occasionally recorded concomitantly to duodenal phase III activity (21,32). Furthermore, 5-HT is also implicated in the regulation of MMC patterns in the abomasum and proximal small intestine (17,(19)(20)(21)27,33), but little is known about the role of the respective 5-HTR subtypes involved in motility control in ruminants.…”

“…However, the serotoninergic pathways were predominantly studied in humans and rodents. The 5-HT was shown to be involved in the initiation and regulation of the myoelectric migrating complex (MMC), in the peristaltic reflex, in the regulation of stomach, small intestine and colon motility, as well as in intestinal secretion (4,9,(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23). The mechanisms of action of 5-HT in the digestive tract are not completely understood and the role of 5-HTR subtypes in the regulation of GI motility differs among species and locations along the GI tract (9,24,25).…”

Ultrasonographic assessment of the reticular motility in cows after administration of different doses of metoclopramide and neostigmine

“…This finding supports the result of Jones et al (1994) that recorded short half-life of metoclopramide and suggested use continuous release device to produce prolonged effect. Metoclopramide is an antagonist at dopaminergic (D2) receptors and a serotonin (5-hydroxytryptamine; 5-HT) agonist at 5-HT4 receptors and antagonist at 5-HT3 receptors (Plaza et al 1996). In humans, it is also a neuroleptic agent that induces extrapyramidal activity with apparent adverse effect, which is more likely to occur in children (Hyams et al 1986;Cézard et al 2003).…”