Role of mast cells in bronchial contraction in nonallergic obstructive lung pathology

The role of mast cells in contractile bronchial smooth muscle activity has been evaluated in a model of chronic obstructive pulmonary disease induced in rats that were intermittently exposed to nitrogen dioxide (NO₂) for 60 days. Starting from the 31st day, one group of rats inhaled sodium cromoglycate before exposure to NO₂ to stabilize mast cell membranes. The second group (control) was not treated. Isometric smooth muscle contraction was analysed in isolated bronchial samples in response to nerve and smooth muscle stimulation. Histological analysis revealed large numbers of mast cells in lung tissue of COPD model rats. The inhibition of mast cell degranulation by sodium cromoglycate prevented the development of nerve-stimulated bronchial smooth muscle hyperactivity in COPD model rats. Histamine or adenosine-induced hyperactivity on nerve stimulation was also inhibited by sodium cromoglycate in bronchial smooth muscle in both control and COPD model rats. This suggests that the mechanism of contractile activity enhancement of bronchial wall smooth muscle cells may be mediated through the activation of resident mast cells transmembrane adenosine receptors resulting in their partial degranulation, with the released histamine acting upon histamine H1-receptors which trigger reflex pathways via intramural ganglion neurons.