Abstract
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.
Sample Population—Bronchial rings from 6 healthy horses and 6 horses affected with SPAOPD.
Procedure—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 concentrationdependent contractile responses in bronchial rings. Prostaglandin F2α induced weak and inconsistent contractile responses. The other 2 agents, norepinephrine and substance P, did not induce concentrationdependent responses. Considering the overall groupdrug 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 and Clinical Relevance—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. (Am J Vet Res 2001;62:259–263).
