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Comparative responses of bronchial rings to mediators of airway hyperreactivity in healthy horses and those affected with summer pastureassociated obstructive pulmonary disease

Changaram S. VenugopalEquine Health Studies Program, Departments of Veterinary Physiology, Pharmacology, and Toxicology, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803.

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 BVSc, PhD
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Rustin M. MooreEquine Health Studies Program, Departments of Veterinary Physiology, Pharmacology, and Toxicology, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803.
Department of Veterinary Clinical Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803.

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Earnestine P. HolmesEquine Health Studies Program, Departments of Veterinary Physiology, Pharmacology, and Toxicology, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803.

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Catherine E. KochEquine Health Studies Program, Departments of Veterinary Physiology, Pharmacology, and Toxicology, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803.

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Thomas L. SeahornDepartment of Veterinary Clinical Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803.
Present address is Hagyard-Davidson-McGee PSC, 4250 Ironworks Pike, Lexington, KY 40511.

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Ralph E. BeadleDepartment of Veterinary Clinical Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803.

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 DVM, PhD

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 F 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).

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 F 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).