Envolvimento de vias capacitativas de cálcio nos efeitos inibitórios do extrato padronizado de Justicia pectoralis na hiperreatividade traqueal induzida por desafio antigênico

Abstract

Justicia pectoralis Jacq. (Acanthaceae) is a plant that has significant amount of coumarin in its composition and is widely used in folk medicine for treatment of respiratory diseases. This study was conducted to test potential pharmacological effects of a standardized extract of J. pectoralis (EPJP) in an animal model of tracheal hyperreactivity. To this end, rats were actively sensitized to ovalbumin (OVA) and submitted or not to OVA challenge to assess the development of smooth muscle hyperreactivity. Stimulated with increasing concentrations of acetylcholine and KCl, rats tracheal rings challenged with OVA was contracted with significantly higher magnitude compared to the non-challenged group. Added directly into the bath chamber containing Ca2+ in free form, EPJP and its main constituent, coumarin, preferably inhibited concentration-effect curves induced by increasing concentrations of KCl or acetylcholine in rat tissues challenged with OVA, compared to those curves made for Ca2+, in the presence of the same agonists in assays performed in medium without Ca2+. After administration by gavage of EPJP or saline, the animals were sacrificed and isolated tracheal preparations were mounted in isolated organ bath chamber, to evaluate contractile response. The hyperresponsive phenotype of the challenged tissue decreased significantly after oral treatment with EPJP. The treatment by gavage abolished changes caused by OVA challenge on levels of inflammatory cytokines IL-1 and TNF-α in bronchoalveolar lavage fluid. In tracheal preparations subjected to depletion of intracellular stores of Ca2+ after repeated stimulation induced by carbachol in the presence of thapsigargin in medium without Ca2+, the EPJP reportedly inhibited the contraction induced by capacitive Ca2+ entry. TRPC proteins subfamily have been charged in these stock mediated Ca2+ currents. Through experiments to determine the expression of some genes associated with the TRPC type proteins, we found that EPJP was able to inhibit the changes in TRPC genes expression caused by antigen challenge. Thus, we can conclude that the pharmacological activity of EPJP in our hyperreactivity model seems to be due to its anti-inflammatory actions. Moreover, EPJP seems to have muscle relaxant activity, with likely involvement of its main constituent, coumarin. Some of these actions may result from the interference of EPJP in contractile mechanisms that recruit Ca2+ influx from the extracellular environment.