Abstract
BackgroundSwine farmers repeatedly exposed to the barn air suffer from respiratory diseases. However the mechanisms of lung dysfunction following repeated exposures to the barn air are still largely unknown. Therefore, we tested a hypothesis in a rat model that multiple interrupted exposures to the barn air will cause chronic lung inflammation and decline in lung function.MethodsRats were exposed either to swine barn (8 hours/day for either one or five or 20 days) or ambient air. After the exposure periods, airway hyper-responsiveness (AHR) to methacholine (Mch) was measured and rats were euthanized to collect bronchoalveolar lavage fluid (BALF), blood and lung tissues. Barn air was sampled to determine endotoxin levels and microbial load.ResultsThe air in the barn used in this study had a very high concentration of endotoxin (15361.75 ± 7712.16 EU/m3). Rats exposed to barn air for one and five days showed increase in AHR compared to the 20-day exposed and controls. Lungs from the exposed groups were inflamed as indicated by recruitment of neutrophils in all three exposed groups and eosinophils and an increase in numbers of airway epithelial goblet cells in 5- and 20-day exposure groups. Rats exposed to the barn air for one day or 20 days had more total leukocytes in the BALF and 20-day exposed rats had more airway epithelial goblet cells compared to the controls and those subjected to 1 and 5 exposures (P < 0.05). Bronchus-associated lymphoid tissue (BALT) in the lungs of rats exposed for 20 days contained germinal centers and mitotic cells suggesting activation. There were no differences in the airway smooth muscle cell volume or septal macrophage recruitment among the groups.ConclusionWe conclude that multiple exposures to endotoxin-containing swine barn air induce AHR, increase in mucus-containing airway epithelial cells and lung inflammation. The data also show that prolonged multiple exposures may also induce adaptation in AHR response in the exposed subjects.
Highlights
Swine farmers repeatedly exposed to the barn air suffer from respiratory diseases
The data showed group differences in percent decrease in Flow@50%Tve1 (Figure 1; P < 0.001). Both 1- and 5-day exposed rats showed increased airway hyper-responsiveness (AHR) compared to controls (P < 0.001) and 20-day exposed (P < 0.05)
We report in vivo and in situ data using an animal model on the effects of single and multiple exposures to the swine barn air
Summary
Swine farmers repeatedly exposed to the barn air suffer from respiratory diseases. the mechanisms of lung dysfunction following repeated exposures to the barn air are still largely unknown. Swine farmers work in confined buildings in close proximity to a large number of pigs and are exposed to toxic gasses such as ammonia and hydrogen sulfide, and to high levels of dust and endotoxins [2]. Exposure to such toxic bio aerosols including endotoxins in the barn air is a risk factor for the development of chronic respiratory symptoms and lung dysfunction [3,4,5]. These data show that a single exposure to the barn air initiates acute lung inflammation
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