Histopathologic alterations induced in the lungs of sheep by use of alpha2-adrenergic receptor agonists.
OBJECTIVE
To study effects of central- and peripheral-acting alpha2-adrenergic receptor agonists on lung parenchyma, platelets, and pulmonary intravascular macrophages (PIM) of sheep.


METHODS
12 healthy mature female sheep.


METHODS
Group-1 (control, n = 2) sheep received 5 ml of physiologic saline solution IV and were euthanatized 3 minutes later. Sheep of group 2 (n = 8) received xylazine (150 microg/kg of body weight, IV), then 2 sheep each were euthanatized 3, 10, or 60 minutes, or 12 hours later. Sheep (n = 2) of group 3 were given ST-91 (30 microg/kg, IV), then were euthanatized 3 minutes later. Immediately after euthanasia, the lungs were fixed intratracheally and tissue was obtained for light and electron microscopy after 1 hour.


RESULTS
Pulmonary parenchymal damage or morphologic alterations in PIM and platelets were not evident in control sheep. Three minutes after xylazine administration, morphologic changes in PIM were appreciable. After 10 minutes, extensive damage to the capillary endothelium and alveolar type-I cells, intra-alveolar hemorrhage, and interstitial and alveolar edema were evident. Most PIM had complete internalization of the surface coat. Similar changes were seen 60 minutes after xylazine administration; however, by 12 hours, morphologic features of PIM and lung parenchyma were almost completely restored. Evidence of PIM activation, obvious damage to capillary endothelium, and extensive pulmonary edema also were evident 3 minutes after ST-91 administration.


CONCLUSIONS
XYLAZINE induces severe pulmonary parenchymal damage when administered at clinical sedative doses in sheep; morphologic changes in PIM within 3 minutes after administration of these drugs are substantial; and platelet aggregation is not apparent.
Department of Biomedical Sciences, Clinical Studies, Ontario Veterinary College, University of Guelph, Canada.
C S
CS
Celly
O S
OS
Atwal
W N
WN
McDonell
W D
WD
Black
D000316:Adrenergic alpha-Agonists / Q000009:adverse effects*; D000818:Animals; D003000:Clonidine / Q000009:adverse effects / Q000031:analogs & derivatives*; D005260:Female; D006993:Hypnotics and Sedatives / Q000009:adverse effects; D008168:Lung / Q000187:drug effects* / Q000473:pathology / Q000648:ultrastructure; D008171:Lung Diseases / Q000139:chemically induced / Q000473:pathology / Q000662:veterinary*; D008264:Macrophages / Q000187:drug effects / Q000648:ultrastructure; D008854:Microscopy, Electron / Q000662:veterinary; D012756:Sheep; D012757:Sheep Diseases / Q000139:chemically induced* / Q000473:pathology; D014991:Xylazine / Q000009:adverse effects*
D000316:Adrenergic alpha-Agonists; D006993:Hypnotics and Sedatives; D014991:Xylazine; C011266:ST 91; D003000:Clonidine