Background

Abnormalities in lung surfactant are well described in human respiratory diseases including asthma, but are poorly described in horses.

Hypothesis

Lung surfactant is abnormal in horses with clinical signs of recurrent airway obstruction (RAO).

Animals

Six healthy horses and 5 horses with RAO.

Methods

Bronchoalveolar lavage fluid (BALF) was obtained from all horses by standard procedures. Cell-free BALF was separated into crude surfactant pellets (CSP) and supernatant via ultracentrifugation. Phospholipid and protein content was analyzed from both of these fractions. Phospholipid composition of CSP was determined using high-performance liquid chromatography with an evaporative light scatter detector. Surface tension of CSP was measured with a pulsating bubble surfactometer.

Results

Compared with healthy horses, surfactant from RAO-affected horses was characterized by significantly decreased phospholipid content in total surfactant (median; range: 23.2; 14.7-62.2 microg/mL BALF versus 172; 111-267 microg/mL BALF, P = .0062) and CSP (20.2; 6.4-48.9 microL/mL BALF versus 155; 94.4-248 microg/mL BALF, P = .0062), and a significantly lower percentage of phosphatidylglycerol (PG) (4.5; 3.6-5.6% versus 6.6; 4.1-7.6%, P = .028). Furthermore, the ratio between the percentages of phosphatidylcholine and PG was significantly higher in RAO-affected horses than in healthy horses (20.9; 16.6: 25.9 versus 13.9; 11.8-22.8, P = .045).

Conclusions and clinical importance

This study demonstrates that surfactant from RAO-affected horses is abnormal. Further studies are needed to determine if these abnormalities are related to an increased tendency for bronchoconstriction and to a decreased ability to clear airway mucus in RAO-affected horses.