title: Isometric responses of isolated intrapulmonary bronchioles from cats with and without adult heartworm infection.
abstract: OBJECTIVE
  To determine the isometric responses of isolated intrapulmonary bronchioles from cats with and without adult heartworm infection.
  
  
  METHODS
  13 purpose-bred adult cats.
  
  
  METHODS
  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 10 μM 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 10 μM 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
  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.
authors.affiliation: Department of Clinical Sciences, College of Veterinary Medicine, Auburn University, Auburn, AL 36849, USA.
authors.forename: Anne A
authors.initials: AA
authors.lastname: Wooldridge
authors.forename: A Ray
authors.initials: AR
authors.lastname: Dillon
authors.forename: D Michael
authors.initials: DM
authors.lastname: Tillson
authors.forename: Qiao
authors.initials: Q
authors.lastname: Zhong
authors.forename: Sharron R
authors.initials: SR
authors.lastname: Barney
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D055745:Bronchioles / Q000187:drug effects / Q000469:parasitology / Q000503:physiopathology*; D001993:Bronchodilator Agents / Q000494:pharmacology; D002371:Cat Diseases / Q000469:parasitology / Q000503:physiopathology*; D002415:Cats; D004183:Dirofilaria immitis / Q000502:physiology*; D004184:Dirofilariasis / Q000469:parasitology / Q000503:physiopathology*; D006632:Histamine / Q000494:pharmacology; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D009119:Muscle Contraction; D009126:Muscle Relaxation; D009130:Muscle, Smooth / Q000187:drug effects / Q000469:parasitology / Q000503:physiopathology*; D009213:Myography / Q000662:veterinary; D009599:Nitroprusside / Q000494:pharmacology; D012701:Serotonin / Q000494:pharmacology; D017366:Serotonin Receptor Agonists / Q000494:pharmacology; D013373:Substance P / Q000494:pharmacology
chemical_list: D001993:Bronchodilator Agents; D017366:Serotonin Receptor Agonists; D009599:Nitroprusside; D012701:Serotonin; D013373:Substance P; D006632:Histamine; D007545:Isoproterenol; D000109:Acetylcholine