Submitted on March 1, 2006
Accepted on November 30, 2006
Early onset airway obstruction in response to organic dust in the horse
Christopher M Deaton1*, Laura Deaton1, Eduard Jose-Cunilleras1, Thea L Vincent2, Alan Baird3, Kirstie Dacre4, and David J Marlin1
1 Department of Physiology, Animal Health Trust, Kentford, United Kingdom
2 Hartpury College, Hartpury, United Kingdom
3 School of Agriculture, Food Science & Veterinary Medicine, University College Dublin, Dublin, Ireland
4 Department of Veterinary Clinical Sciences, Royal (Dick) School of Veterinary Studies, Easter Bush, Midlothian, United Kingdom
* To whom correspondence should be addressed. E-mail: chrisdeaton{at}googlemail.com.
Equine recurrent airway obstruction (RAO) has been used as a naturally occurring model of human asthma. However, it is unknown if there is an early phase response in RAO. The aim of this study was to determine if exposure to organic dust induces immediate changes in lung function in RAO-affected horses, which could be mediated by airway mast cells. Six RAO-affected horses in remission and 6 control horses were challenged with hay-straw dust suspension by nebulisation. Total respiratory resistance at 1Hz, measured by forced oscillation, was increased from 0.62±0.09cmH2O/l/s (mean±SE) to 1.23±0.20cmH2O/l/s 15min after nebulisation in control horses (P=0.023), but did not change significantly in the RAO group. Total respiratory reactance at 1Hz (P=0.005) was significantly lower in the control horses (-0.77±0.07 cmH2O/l/s) compared to the RAO group (-0.49±0.04cmH2O/l/s) 15min after nebulisation. BALF histamine concentration was significantly elevated 10 and 20min post-nebulisation in control horses, but not in RAO horses. Minimum reactance at 1Hz in the early post-nebulisation period significantly correlated with both pre-challenge BALF mast cell numbers (r=-0.65, P=0.02) and peak BALF histamine concentration post-nebulisation (r=-0.61, P=0.04). In conclusion, RAO horses, unlike human asthmatics, do not exhibit an early phase response. However, healthy control horses do demonstrate a mild but significant early (<20min) phase response to inhaled organic dust. This response may serve to decrease the subsequent dose of dust inhaled and as such provide a protective mechanism, which may be compromised in RAO horses.
