Central and peripheral serotonergic control of forestomach motility in sheep.
Participation of tryptaminergic receptors in the control of forestomach motility was investigated in conscious sheep using strain-gauges and chronically implanted electrodes. Two hours after feeding the sheep, serotonin (5-HT) was infused into the jugular vein (i.v.), or the carotid artery (i.c.), or into the lateral cerebral ventricles (i.c.v.), over a 10-min period. An i.v. dose of 16 micrograms/kg/min abolished the cyclic propagated contractions throughout the forestomach, increased ruminoreticular tone, and induced simultaneous contractions of all the parts of the rumen. A dose of 1.6 micrograms/kg/min i.c. or i.v. 5-HT inhibited phasic contractions. The effects of 5-HT were blocked completely by i.c.v. administration of methysergide (20 micrograms/kg) and imipramine (200 micrograms/kg), and blocked partially by naloxone (25 micrograms/kg), but unaffected by atropine (50 micrograms/kg). The inhibitory effects of i.v. 5-HT were antagonized by methysergide (200 micrograms/kg, i.v.) but unaffected by imipramine (2 mg/kg, i.v.) and atropine (250 micrograms/kg, i.v.). Only the i.v. administration of methysergide blocked the inhibition induced by i.c. infusion (1.6 micrograms/kg/min) of 5-HT. It is suggested that 5-HT exhibits an inhibitory control on forestomach phasic contractions through hypothalamic and bulbar 5-HT receptors, and exerts peripheral excitatory effects on the tone of the rumen wall.
D000818:Animals; D001285:Atropine / Q000494:pharmacology; D004594:Electrophysiology; D005260:Female; D005769:Gastrointestinal Motility / Q000187:drug effects; D007099:Imipramine / Q000494:pharmacology; D007275:Injections, Intravenous; D007276:Injections, Intraventricular; D008784:Methysergide / Q000494:pharmacology; D009270:Naloxone / Q000494:pharmacology; D011976:Receptors, Muscarinic / Q000187:drug effects; D011957:Receptors, Opioid / Q000187:drug effects; D012701:Serotonin / Q000502:physiology*; D012702:Serotonin Antagonists / Q000494:pharmacology; D012756:Sheep / Q000502:physiology*; D013279:Stomach, Ruminant / Q000502:physiology*
D011976:Receptors, Muscarinic; D011957:Receptors, Opioid; D012702:Serotonin Antagonists; D012701:Serotonin; D009270:Naloxone; D001285:Atropine; D007099:Imipramine; D008784:Methysergide