J. Vet. Med. zyxwvut A. 42, 443-451 (1995) zyxwvut 0 1995 Blackwell Wissenschafts zyxwvu - Verlag, Berlin ISSN 0931-1 84X zyxwvuts Department of Veterinary Physiology and Biochemistry, U. C.D. Veterinary College, Dublin zy The Effects of Intracoeliac Injections of Alpha-adrenergic Agonists and Veratridine on Reticuloruminal Motility and the Evocation of Rumination in Sheep D. P. CAMPION and B. F. LEEK Address of Authors: Department of Veterinary Physiology and Biochemistry, U. C. D. Veterinary College, Dublin, Ireland With zyxwvu 3 jigwres and 1 table (Received zyxwv for publication March 20, f995) Summary The ability of alpha-2 adrenoreceptor agonists and veratridine to evoke rumination and to modify reticular motility in adult Suffolk-cross sheep when injected by close-arterial injection into the forestomach was investigated. The specific alpha-2 adrenoreceptor agonists, xylazine and medetomidine, evoked rumination and increased reticular motility. The Na+ channel activator veratridine also evoked rumination and dramatically increased reticular motility. In contrast, injection of the alpha-1 adrenoreceptor agonist, phenylephrine, was ineffectual in evoking rumination and resulted in reduced reticular motility. It is concluded that the evocation of rumination by alpha-2 adrenergic agonists and veratridine is probably due to the activation of sensory nervous receptors (epithelial receptors) located in the reticulorumen. Introduction Rumination in conscious sheep occurs if the brain receives an adequate peripheral excitatory drive from fibrous digesta in the reticulorumen. The demonstration by KAY zy (1959) that adrenaline or noradrenaline injected into the jugular vein caused rumination indicated that rumination could also be evoked by pharmacological stimulation. It has since been established that adrenaline evoked rumination by acting on uyadreno- receptors (LEEK and STAFFORD, 1987) located in the area supplied by the coeliac artery, probably the forestomach (LEEK and STAFFORD, 1986). KAY (1959) further suggested that adrenaline acted to evoke rumination by sensitising nervous sensory receptors located in the forestomach. The experiments described in this paper were carried out as part of an intensive ongoing study to elucidate further the mechanism by which a*- adrenergic agents evoke rumination. To this end the effects of close arterial injection of both adrenergic agonists and the neuroeffector veratridine were assessed. Materials and Methods Permanent ruminal cannulae were fitted under aseptic conditions in 13 adult Suffolk-cross sheep (body weight 65-80 kg) using the method described by LEEK (1976). General anaesthesia U.S. Copyright Clearance Center Code Statement: 0931 - 184x195 /4207 - 0443f11 .oo /o