Early onset airway obstruction in response to organic dust in the horse.
Equine recurrent airway obstruction (RAO) has been used as a naturally occurring model of human asthma. However, it is unknown whether there is an early-phase response in RAO. The aim of this study was to determine whether 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 six control horses were challenged with hay-straw dust suspension by nebulization. Total respiratory resistance at 1 Hz, measured by forced oscillation, was increased from 0.62 +/- 0.09 cmH(2)O.l(-1).s (mean +/- SE) to 1.23 +/- 0.20 cmH(2)O.l(-1).s 15 min after nebulization in control horses (P = 0.023) but did not change significantly in the RAO group. Total respiratory reactance at 1 Hz (P = 0.005) was significantly lower in the control horses (-0.77 +/- 0.07 cmH(2)O.l(-1).s) than in the RAO group (-0.49 +/- 0.04 cmH(2)O.l(-1).s) 15 min after nebulization. Bronchoalveolar lavage fluid (BALF) histamine concentration was significantly elevated 10 and 20 min postnebulization in control horses but not in RAO horses. Minimum reactance at 1 Hz in the early postnebulization period significantly correlated with both prechallenge BALF mast cell numbers (r = -0.65, P = 0.02) and peak BALF histamine concentration postnebulization (r = -0.61, P = 0.04). In conclusion, RAO horses, unlike human asthmatic patients, do not exhibit an early-phase response. However, healthy control horses do demonstrate a mild but significant early (<20 min) 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.
Deaton
Christopher M
CM
Dept. of Physiology, Animal Health Trust, Lanwades Park, Kentford, Suffolk CB8 7UU, UK.
Deaton
Laura
L
Jose-Cunilleras
Eduard
E
Vincent
Thea L
TL
Baird
Alan W
AW
Dacre
K
K
Marlin
David J
DJ
D000818:Animals; D001985:Bronchial Provocation Tests / Q000662:veterinary; D001992:Bronchoalveolar Lavage Fluid / Q000737:chemistry / Q000166:cytology; D004391:Dust; D005260:Female; D006632:Histamine / Q000032:analysis; D006734:Horse Diseases / Q000503:physiopathology*; D006736:Horses; D007249:Inflammation / Q000503:physiopathology / Q000662:veterinary*; D008173:Lung Diseases, Obstructive / Q000503:physiopathology / Q000662:veterinary*; D008297:Male; D008407:Mast Cells / Q000502:physiology*; D012129:Respiratory Function Tests / Q000662:veterinary
D004391:Dust; D006632:Histamine