Responses of equine trachealis and lung parenchyma to methacholine, histamine, serotonin, prostanoids, and leukotrienes in vitro

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Abstract
The responses of equine trachealis and lung parenchymal strips to a range of contractile agonists were studied. Equine trachealis responded to methacholine > histmaine > serotonin as shown by the maximal responses but failed to respond to either leukotrienes (LT), prostaglandin F2.alpha., or U-44069. Equine parenchymal strips showed considerable tonal activity and responded to LTD4 .simeq. LTC4 > U-44069 = LTE4 > methacholine.simeq.histamine .simeq. serotonin > prostaglandin F2.alpha. as determined through pD2 valeus. Neither the concentration response curve to LTD4 nor the intrinsic tonal activity of the preparations was modified by pretreatment with either atropine or indomethacin, although the maximal response to LTD4 was reversed by addition of the LTD4 receptor antagonist, MK-571. Thus arachidonic acid metabolites, including LTs, must be considered potential mediators of equine small airway disease, a potential model of human bronchial asthma.