Characterization of endothelin receptors in the peripheral lung tissues of horses unaffected and affected with recurrent airway obstruction.

The purpose of the study was to determine and compare the expression of endothelin (ET) receptors in the peripheral lungs of healthy horses and those affected with recurrent airway obstruction (RAO) using reverse transcriptase polymerase chain reaction (RT-PCR), real-time PCR, Western blot analysis, and immunohistochemical techniques. Two groups of horses (7 healthy and 7 RAO-affected) were selected from a pool of horses destined for euthanasia. The grouping of horses was based on the history, clinical scoring, and pulmonary function testing. After euthanasia, gross postmortem evaluation of the lungs was conducted, and lung samples were collected and either stored at -80 degrees C or fixed in zinc-formalin for 12 h. The RT-PCR was performed by using specific primers for ETA and ETB receptors, and beta-actin. To determine the relative gene expression real-time PCR was performed. To detect ET receptor protein expression, Western blotting and immunohistochemical studies were performed using polyclonal antibodies against ETA and ETB receptors and beta-actin. The ET receptor expression was determined by performing either densitometric analyses or scoring of immunostaining. Statistical analyses were performed to detect differences in receptor expression within and between the 2 groups. The results indicated that ET receptor expression, particularly ETB receptors, was significantly greater in the peripheral lungs of RAO-affected horses than in those of healthy horses. Clinical trials using ET receptor antagonists, particularly ETB antagonists might help in developing a therapeutic strategy to treat this career-ending disease.