title: Effects of diet and osmotic pressure on Na+ transport and tissue conductance of sheep isolated rumen epithelium.
abstract: The intention of this study was to determine the effects of mucosal osmotic pressure on transport and barrier functions of the rumen epithelium of sheep, which were fed various diets: hay ad libitum, or 600, 1200 or 1800 g day(-1) of a supplemented diet plus hay ad libitum. The experiments were conducted by using the conventional Ussing chamber technique. Mucosal osmolarity was adjusted to 300 (control), 375 or 450 mosmol l(-1). Feeding of a supplemented diet led to a significant increase of mucosal to serosal Na+ transport and net Na+ transport, probably because of an increase of apical Na+-H+ exchange activity. An increase in mucosal osmotic pressure: (a) reduced net Na+ transport in all feeding groups, the remaining net Na+ transport being higher in tissues of sheep fed a supplemented diet; (b) increased transepithelial tissue conductance, this rise being smallest with a high intake of the supplemented diet; and (c) enhanced the serosal to mucosal Na+ transport in tissues of hay-fed sheep and sheep fed with 600 g day(-1) of the supplemented diet, while higher intakes of the supplemented diet (1200 and 1800 g) did not produce any effect. All these changes indicate a diet-dependent adaptation to luminal hypertonicity.
authors.affiliation: Department of Veterinary Physiology, Faculty of Veterinary Medicine, Freie Universität Berlin, Oertzenweg 19b, 14163 Berlin, Germany. lodemann@zedat.fu-berlin.de
authors.forename: Ulrike
authors.initials: U
authors.lastname: Lodemann
authors.forename: Holger
authors.initials: H
authors.lastname: Martens
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology; D000821:Animal Feed; D000818:Animals; D001693:Biological Transport, Active / Q000502:physiology; D004032:Diet / Q000379:methods*; D019587:Dietary Supplements; D004848:Epithelium / Q000502:physiology*; D066298:In Vitro Techniques; D009997:Osmotic Pressure; D010539:Permeability; D012417:Rumen / Q000502:physiology*; D012756:Sheep / Q000502:physiology*; D012964:Sodium / Q000378:metabolism*
chemical_list: D012964:Sodium