Isometric responses of isolated intrapulmonary bronchioles from cats with and without adult heartworm infection

Objective: To determine the isometric responses of isolated intrapulmonary bronchioles from cats with and without adult heartworm infection. Animals: 13 purpose-bred adult cats. Procedures: Cats were infected with 100 third-stage larvae or received a sham inoculation, and the left caudal lung lobe w...

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Published in:	American journal of veterinary research Vol. 73; no. 3; pp. 439 - 446
Main Authors:	Wooldridge, Anne A, Dillon, A. Ray, Tillson, D. Michael, Zhong, Qiao, Barney, Sharron R
Format:	Journal Article
Language:	English
Published:	United States 01-03-2012
Subjects:	acetylcholine Acetylcholine - pharmacology adults agonists Animals Bronchioles - drug effects Bronchioles - parasitology Bronchioles - physiopathology Bronchodilator Agents - pharmacology Cat Diseases - parasitology Cat Diseases - physiopathology Cats Dirofilaria immitis - physiology Dirofilariasis - parasitology Dirofilariasis - physiopathology heartworms histamine Histamine - pharmacology In Vitro Techniques Isoproterenol - pharmacology larvae Muscle Contraction Muscle Relaxation Muscle, Smooth - drug effects Muscle, Smooth - parasitology Muscle, Smooth - physiopathology Myography - veterinary nitroprusside Nitroprusside - pharmacology respiratory system serotonin Serotonin - pharmacology Serotonin Receptor Agonists - pharmacology smooth muscle substance P Substance P - pharmacology
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Summary:	Objective: To determine the isometric responses of isolated intrapulmonary bronchioles from cats with and without adult heartworm infection. Animals: 13 purpose-bred adult cats. Procedures: Cats were infected with 100 third-stage larvae or received a sham inoculation, and the left caudal lung lobe was collected 278 to 299 days after infection. Isometric responses of intrapulmonary bronchiolar rings were studied by use of a wire myograph. Three cycles of contractions induced by administration of 10μM acetylcholine were followed by administration of the contractile agonists acetylcholine, histamine, and 5-hydroxy-tryptamine. To evaluate relaxation, intrapulmonary bronchiolar rings were constricted by administration of 10μM 5-hydroxytryptamine, and concentration-response curves were generated from administration of sodium nitroprusside, isoproterenol, and substance P. Results: Compared with tissues from control cats, contractile responses to acetylcholine and 5-hydroxytryptamine were reduced in tissues from heartworm-infected cats. Relaxation to isoproterenol was significantly reduced in tissues from heartworm-infected cats. Relaxation to substance P was increased in tissues from heartworm-infected cats, but relaxation to sodium nitroprusside was unchanged. Conclusions and Clinical Relevance: Results suggested that despite increased bronchiolar wall thickness in heartworm-infected cats, a hyperreactive response of the bronchiolar smooth muscle is not the primary mechanism of respiratory tract clinical signs. Reduced response of the airway to isoproterenol may indicate refractoriness to bronchiolar relaxation in heartworm-infected cats.
Bibliography:	http://dx.doi.org/10.2460/ajvr.73.3.439 ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23
ISSN:	0002-9645 1943-5681
DOI:	10.2460/ajvr.73.3.439