Central and peripheral beta-adrenergic influences on reticulo-rumen and upper-gut myoelectrical activity in sheep.
The effects of intravenous (i.v.) and intracerebroventricular (i.c.v.) administration of beta-adrenoceptor agonists were evaluated on the reticulo-rumen and upper-gut myoelectrical activity in six ewes chronically fitted with intraparietal electrodes and a cannula in a lateral ventricle of the brain. Intravenous infusion of the beta 1 agonist dobutamine (30 micrograms/kg/min for 15 min) reduced the frequency of reticulo-ruminal and abomasal contractions and stimulated duodeno-jejunal motility, inducing a Phase III on the jejunum. These effects were reproduced by i.c.v. dobutamine at a dose of 10 micrograms/kg. Intravenous infusion of the beta 2 agonist ritodrine (15 micrograms/kg/min for 15 min) selectively inhibited antral and duodenal motility. Ritodrine i.c.v. (15 micrograms/kg) did not affect forestomach or gastrointestinal motility. The mixed beta 1, beta 2 agonist isoprenaline infused i.v. (0.6 micrograms/kg/min for 15 min) reproduced the effects of i.v. dobutamine, except at the antro-duodenal level which was strongly inhibited. The effects of i.v. dobutamine were antagonized by i.v. or i.c.v. acebutolol, a specific beta 1 antagonist. The effects of i.v. ritodrine were blocked by i.v. but not i.c.v. administration of propranolol, a mixed beta 1, beta 2 antagonist. These data indicate that the stimulation of central beta 1 adrenoceptors inhibits forestomach and antral motility and stimulates duodeno-jejunal motility. Stimulation of peripheral beta 2 adrenoceptors selectively inhibits duodeno-jejunal motility.
Brikas
P
P
Department of Pharmacology, INRA, Toulouse, France.
Buéno
L
L
Fioramonti
J
J
D000070:Acebutolol / Q000494:pharmacology; D000818:Animals; D004280:Dobutamine / Q000494:pharmacology; D004386:Duodenum / Q000187:drug effects / Q000502:physiology; D004576:Electromyography; D005260:Female; D005769:Gastrointestinal Motility / Q000187:drug effects; D007421:Intestine, Small / Q000187:drug effects / Q000502:physiology*; D007545:Isoproterenol / Q000494:pharmacology; D007583:Jejunum / Q000187:drug effects / Q000502:physiology; D011433:Propranolol / Q000494:pharmacology; D011943:Receptors, Adrenergic, beta / Q000502:physiology*; D012159:Reticulum / Q000187:drug effects / Q000502:physiology*; D012312:Ritodrine / Q000494:pharmacology; D012417:Rumen / Q000187:drug effects / Q000502:physiology*; D012756:Sheep / Q000502:physiology*
D011943:Receptors, Adrenergic, beta; D004280:Dobutamine; D000070:Acebutolol; D011433:Propranolol; D012312:Ritodrine; D007545:Isoproterenol