Abstract: We investigated the impact of respiratory syncytial virus (RSV) infection, an important asthma precipitant, on endothelin receptor function and release in sheep bronchial explants. RSV infection was confirmed using polymerase chain reaction and immunohistochemistry. Since sheep airway smooth muscle contains only endothelin-A receptors, sarafotoxin (Stx) S6c did not cause airway contraction. In contrast, sarafotoxin S6c (300 nM) caused contraction in RSV-infected bronchial explants (8 ± 3% carbachol E max ). However, we could not detect airway smooth muscle endothelin-B receptors in explants using autoradiography. RSV infection per se did not alter the release of immunoreactive endothelin from sheep bronchial explants (control = 11.6 ± 0.9 pg versus RSV = 12.1 ± 0.9 pg). Interestingly, dexamethasone (1 μM) alone increased endothelin release in both control (17.9 ± 2.0 pg) and RSV-infected tissue (18.3 ± 3.1 pg). The combined presence of protease-activated receptor-2 (PAR-2) ligand (100 μM) and dexamethasone (1 μM) also increased endothelin release from control tissue (17.3 ± 1.4 pg), but endothelin release was suppressed by PAR-2 ligand in RSV-infected tissue (10.3 ± 0.8 pg), probably because PAR-2 expression was increased by RSV. In summary, the novel expression of endothelin-B receptors triggered by RSV might be relevant to RSV-associated asthma. Furthermore, activation of airway PAR-2 may be protective in asthma where endothelin levels are elevated in part via endothelin release suppression. Key Words: respiratory syncytial virus, endothelin, bronchial explants, airway smooth muscle (J Cardiovasc Pharmacol™ 2004;44(suppl 1):S202–S206) R espiratory tract viral infections commonly precipitate and exacerbate asthma symptoms. Indeed, 85% of asthma exacerbations in children and about 50% of asthma- like symptoms in adults involve respiratory tract viral infection. 1 Most children have been infected with respiratory syncytial virus (RSV) by the age of 2 years. The development of bronchiolitis associated with RSV infection in infants under the age of 1 years has been associated with an increased risk for developing asthma. 2 There is a wealth of evidence to suggest that endothelin (ET)-1 plays a mediator role in asthma. Importantly, in asthma, immunoreactive ET levels are increased in airway epithelium and in bronchoalveolar lavage fluid. In addition, ET-1 is a potent bronchoconstrictor, a secretagogue for bronchial mucous and an airway smooth muscle mitogen. ET-1 also has pro-inflammatory actions in the airways, stimulating the release of inflammatory cytokines. 3 We have previously shown that respiratory tract viral infection with parainfluenza-1, 4 parainfluenza-3 5 and influenza-A 6 is associated with changes in ET receptor function and distribution in airway smooth muscle. We have also shown that influenza-A virus infection with associated airway inflammation markedly increased ET production in mouse airways. 7 Importantly, RSV infection of airway epithelial cells in culture significantly increased the expression of ET-1 mRNA. 8 Lambs inoculated with a human strain of RSV develop clinical signs of respiratory tract infection with an immunological response to RSV present in the airways. 9 We have developed an airway explant culture system using sheep bronchi in order to establish infection with RSV. 10 The current study examined the impact of RSV infection on ET receptor function and distribution in sheep bronchial explants. In addition, the release of immunoreactive ET from control and RSV-infected bronchial explants was investigated. METHODS Explant Culture Sheep (female and castrated male Merinos, 1–10 months old) were sacrificed by an experienced animal care technician using a captive bolt and were exsanguinated before the lungs were removed. Bronchial rings (3–6 mm, internal diameter) were obtained and explants established. 10 Bronchial rings were placed individually in 35-mm plastic culture dishes containing 2 mL serum-free CMRL 1066 S202 J Cardiovasc Pharmacol™ • Volume 44, Supplement 1, November 2004 SUPPLEMENT ARTICLE The Impact of Respiratory Syncytial Virus Infection on Endothelin Receptor Function and Release in Sheep Bronchial Explants Lynette B. Fernandes*, Angela C. D’Aprile*, Glenn J. Self*, Gerald B. Harnett†, and Roy G. Goldie* *Pharmacology Unit, School of Medicine & Pharmacology, The University of Western Australia and Western Australian Institute for Medical Research, Perth, Western Australia, Australia, and †Department of Microbiology and Infectious Diseases, The Western Australian Centre for Pathology and Medical Research, Perth, Western Australia, Australia Address correspondence and reprint requests to Dr Lynette Fernandes, Pharmacology Unit (M510), School of Medicine and Pharmacology, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia. E-mail: lfernandes@pharm.uwa.edu.au This work was supported by the Asthma Foundation of Western Australia Inc. Copyright ©2004 by Lippincott Williams & Wilkins