Comparative responses of bronchial rings to mediators of airway hyperreactivity in healthy horses and those affected with summer pasture-associated obstructive pulmonary disease.
OBJECTIVE
To compare responses of bronchial rings obtained from healthy horses and horses affected with summer pasture-associated obstructive pulmonary disease (SPAOPD) to selected mediators of airway hyperreactivity in vitro.


METHODS
Bronchial rings from 6 healthy horses and 6 horses affected with SPAOPD.


METHODS
Bronchial rings obtained from each group of horses were mounted in organ baths and attached to force transducers interfaced with a polygraph. After applying 2g of tension, each ring was allowed to equilibrate for 45 minutes in Tyrode's solution at 37 C. Cumulative concentration-response relationships to graded concentrations of selected mediators (10(-8) to 10(-4) M) were determined and analyzed for significance at each concentration.


RESULTS
Acetylcholine, histamine, 5-hydroxytryptamine, and leukotriene D4 induced concentration-dependent contractile responses in bronchial rings. Prostaglandin F2alpha induced weak and inconsistent contractile responses. The other 2 agents, norepinephrine and substance P, did not induce concentration-dependent responses. Considering the overall group-drug effect, acetylcholine, histamine, 5-hydroxytryptamine, and leukotriene D4 were effective in inducing consistent concentration-dependent contractile responses in both groups. Only 5-hydroxytryptamine and histamine induced significant responses in contractility between groups. The response of bronchial rings from horses with SPAOPD to 5-hydroxytryptamine was significantly greater than those from control horses, whereas the response to histamine was significantly lower. Significant responses were evident at concentrations ranging from 10(-6) to 10(-4) M for both drugs.


CONCLUSIONS
Because the airways of horses with SPAOPD had increased responsiveness to 5-hydroxytryptamine in vitro, treatment modalities using 5-hydroxytryptamine antagonists should be investigated to address this phenomenon.
Venugopal
C S
CS
Equine Health Studies Program, Department of Veterinary Physiology, School of Veterinary Medicine, Louisiana State University, Baton Rouge 70803, USA.
Moore
R M
RM
Holmes
E P
EP
Koch
C E
CE
Seahorn
T L
TL
Beadle
R E
RE
D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D001980:Bronchi / Q000187:drug effects* / Q000503:physiopathology; D016535:Bronchial Hyperreactivity / Q000503:physiopathology / Q000662:veterinary*; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D006632:Histamine / Q000494:pharmacology; D006734:Horse Diseases / Q000503:physiopathology*; D006736:Horses; D066298:In Vitro Techniques; D018836:Inflammation Mediators / Q000494:pharmacology*; D017998:Leukotriene D4 / Q000494:pharmacology; D008173:Lung Diseases, Obstructive / Q000503:physiopathology / Q000662:veterinary*; D009119:Muscle Contraction / Q000187:drug effects; D012621:Seasons; D012701:Serotonin / Q000494:pharmacology
D018836:Inflammation Mediators; D012701:Serotonin; D017998:Leukotriene D4; D006632:Histamine; D000109:Acetylcholine