title: Involvement of alpha-adrenoreceptors in the regulation of omasal cyclic myoelectrical activity in sheep.
abstract: In five conscious adult ewes at rest, chronically implanted with electrodes in the musculature of the omasal wall, intravenous (i.v.) infusion for 30 min of alpha 1- or alpha 2-adrenergic receptor blockers, prazosin (20 micrograms/kg/min) and yohimbine (30 micrograms/kg/min), respectively, had no significant effects on omasal myoelectrical activity. The i.v. administration for 15 min of alpha 1- or alpha 2-agonists phenylephrine (4 micrograms/kg/min) or naphazoline (2.5 micrograms/kg/min), respectively, increased the frequency and the amplitude of groups of myoelectrical discharges of omasum, as well as the duration of its activity. Pretreatment of animals with prazosin blocked the responses to phenylephrine. Yohimbine prevented the effects of naphazoline dose-dependently. It is suggested that both alpha 1- and alpha 2-adrenoreceptors are involved in regulation of the sheep's omasal notility. This regulation did not seem to be a simple consequence of the changes in the reticular motility.
authors.affiliation: Laboratory of Physiology, Veterinary Faculty, Aristotelian University, Thessaloniki, Greece.
authors.forename: P
authors.initials: P
authors.lastname: Brikas
mesh_terms: D000818:Animals; D004566:Electrodes / Q000662:veterinary; D004576:Electromyography / Q000662:veterinary; D005260:Female; D009278:Naphazoline / Q000037:antagonists & inhibitors / Q000494:pharmacology; D009851:Omasum / Q000187:drug effects / Q000502:physiology*; D010656:Phenylephrine / Q000037:antagonists & inhibitors / Q000494:pharmacology; D011224:Prazosin / Q000494:pharmacology; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects / Q000502:physiology*; D012756:Sheep / Q000502:physiology*; D015016:Yohimbine / Q000494:pharmacology
chemical_list: D011942:Receptors, Adrenergic, alpha; D010656:Phenylephrine; D015016:Yohimbine; D009278:Naphazoline; D011224:Prazosin