Early onset airway obstruction in response to organic dust in the horse

Abstract

Deaton CM, Deaton L, Jose-Cunilleras E, Vincent TL, Baird AW, Dacre K, Marlin DJ. Early onset airway obstruction in response to organic dust in the horse. J Appl Physiol 102: [1071][1072][1073][1074][1075][1076][1077] 2007. First published December 7, 2006; doi:10.1152/japplphysiol.00264.2006.-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 Ϯ 0.09 cmH 2O ⅐ l Ϫ1 ⅐ s (mean Ϯ SE) to 1.23 Ϯ 0.20 cmH2O ⅐ l Ϫ1 ⅐ s 15 min after nebulization in control horses (P ϭ 0.023) but did not change significantly in the RAO group. Total respiratory reactance at 1 Hz (P ϭ 0.005) was significantly lower in the control horses (Ϫ0.77 Ϯ 0.07 cmH2O ⅐ l Ϫ1 ⅐ s) than in the RAO group (Ϫ0.49 Ϯ 0.04 cmH2O ⅐ l Ϫ1 ⅐ 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 ϭ Ϫ0.65, P ϭ 0.02) and peak BALF histamine concentration postnebulization (r ϭ Ϫ0.61, P ϭ 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 (Ͻ20 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. equine; lung function; allergen HUMAN ASTHMATIC PATIENTS develop an early-phase bronchoconstriction within minutes of exposure to inhaled allergens.

Evaluation of the effects of the R- and S-enantiomers of salbutamol on equine isolated bronchi

“…In conclusion, our studies demonstrated that S-salbutamol elicited a weak contraction of equine airway smooth muscle, but induced a significant hyperresponsiveness to histamine that could be detrimental particularly in RAO-affected horses [27][28][29][30]. Our results suggest that it may be prudent to administrate the R-isomer alone in RAO horses to avoid detrimental effect of S-isomer.…”

Heaves, an asthma‐like disease of horses

“…An immediate allergic response is not typically associated with heaves exacerbation and an early phase (10–20 min) histamine release and bronchoconstriction response to inhaled dust does not occur in diseased horses 46 . A significant histamine release and bronchoconstriction is however reported in healthy controls, suggesting that the early phase response may contribute to reduce the amounts of antigens reaching the peripheral airways and therefore be protective 46 .…”

“…An immediate allergic response is not typically associated with heaves exacerbation and an early phase (10–20 min) histamine release and bronchoconstriction response to inhaled dust does not occur in diseased horses 46 . A significant histamine release and bronchoconstriction is however reported in healthy controls, suggesting that the early phase response may contribute to reduce the amounts of antigens reaching the peripheral airways and therefore be protective 46 . Nevertheless, pulmonary mast cells from heaves‐affected horses have a greater in vitro histamine release in response to mould extracts ( A. fumigatus , M. feani , A. tenius ) 47 and greater histamine concentrations are detected in pulmonary epithelial lining fluid from these horses compared with controls 5 h, but not 30 min, after natural antigenic challenge 48 .…”

Study on bronchoconstriction induced by histamine or serotonin in “Precision Cut Lung Slices” of the horse

“…Only in healthy horses an immediate allergic reaction can be seen (Deaton et al 2007). This suggests that the reaction of a healthy horse to an inhaled allergen is a protective mechanism which avoids the distribution of the allergen in small airways.…”