Interactions among Three Classes of Mediators Explain Antigen-Induced Bronchoconstriction in the Isolated Perfused and Ventilated Guinea Pig Lung

Abstract

Intravascular challenge of isolated perfused and ventilated guinea pig lung (IPL) from actively sensitized guinea pigs, with cumulatively increasing (10-10,000 g) doses of ovalbumin (OVA), resulted in dose-dependent and reproducible reductions in lung conductance. The antihistamines mepyramine (1 M) and metiamide (1 M), the leukotriene antagonist zafirlukast (0.1 M), or the cyclooxygenase enzyme (COX) inhibitor diclofenac (10 M) each caused a parallel and rightward shift in the dose-response relation for OVA, providing evidence for contributions of histamine, cysteinyl-leukotrienes, and COX products to the OVA-induced bronchoconstriction in the IPL. Moreover, when all three drugs were combined there was a complete abolishment of the response to OVA. When two antagonists or inhibitors were combined, the results, however, were more complex. The 5-lipoxygenase inhibitor BAY x1005 (30 M) and the thromboxane (TP) receptor antagonist BAY u3405 (1 M) given as single treatment did not inhibit the response to OVA. However, combinations of different antagonists/inhibitors, including BAY x1005 and BAY u3405, caused pronounced inhibitions of the antigen responses, suggesting synergism in action. On the basis of these data it was concluded that although histamine and cysteinyl-leukotrienes mediate the major part of the bronchoconstriction, one or several prostanoids other than thromboxane contribute to the bronchoconstriction evoked by OVA. Moreover, the effect of diclofenac involved a dual action because it also made the IPL less sensitive to histamine and LTD 4 . The findings resemble and extend recent observations in clinical studies of patients with asthma and support the usefulness of this particular model in airway pharmacology.

Characterisation of guinea pig precision-cut lung slices: comparison with human tissues

“…The combination of the antihistamine with either TP or cysteinyl-leukotriene antagonists was particularly effective. In general, these results are in line with previous findings in other GP preparations such as perfused lungs [7], isolated tracheas [34] or parenchymal strips [30], which also show that histamine, leukotrienes and cyclo-oxygenase products contribute additively to allergen-induced bronchoconstriction. Those studies, however, employed cyclo-oxygenase inhibitors rather than TP receptor antagonists; in comparison, it appears that when given alone, cyclo-oxygenase inhibitors are more effective than TP receptor antagonists.…”

“…Nonetheless, all these experimental studies show that allergen-induced bronchoconstriction can only be significantly prevented if at least two of three bronchoactive mast cell mediators are blocked. In atopic subjects with asthma, antileukotriene drugs effectively inhibit both the early and late phases of allergen-induced bronchoconstriction [7,30]. This may seem to contrast with the current authors' inability to find a pronounced effect of the cysLT 1 receptor antagonist montelukast alone in the GP PCLS model.…”

“…GPs are frequently employed for studies in pulmonary pharmacology, because they are thought to possess a pharmacological profile [6,7,30] similar to that of humans [31,32]. The number of independent experiments was as follows: control n512; Tripro n58; SQ n58; Monte n55; Tripro + SQ n54; Tripro + Monte n55; SQ + Monte n55;…”

“…Passive sensitisation GP PCLS were treated and incubated overnight with 1% serum from GPs that had been actively sensitised with ovalbumin using standard protocols [7]. The next day, slices were transferred onto a 24-well plate with fresh medium and put under the microscope.…”

“…For instance, rodent airways do not respond or respond only weakly to leukotrienes [1], mediators that readily cause bronchoconstriction in humans [2] and guinea pigs (GPs) [3,4]. GPs, which are not rodents [5], are widely used in pulmonary pharmacology, because their airways' responsiveness to mediators and drugs is thought to resemble human airways more closely than those of mice or rats [6,7]. However, most studies have focused either on in vivo experiments or on large airway preparations, both of which are difficult to translate to studies with humans, making direct interspecies comparisons difficult.…”