The lack of compound 48/80-induced contraction in isolated trachea of mastcell-deficient Ws/Ws rats in vitro: the role of connective tissue mast cells

In the rat trachea, two types of mast cells have been identified, connectiv e tissue mast cells and mucosal mast cells. Their different characteristics may account for their different biological functions. The role of connecti ve tissue mast cells in tracheal contraction as one feature of the immediat e reaction of asthma was studied in vitro in isolated trachea, using tissue derived from mast cell-deficient (Ws/Ws) rats, heterozygous (Ws/+) rats an d control (+/+) rats, and compound 48/80 as a potent inducer of mast cell d egranulation. The contractile response of tracheas from the three types of rats was also studied upon exposure to the following spasmogens: histamine, 5-hydroxytryptamine (5-HT), and carbachol. Histamine content in tissues re flected the differing mast cell numbers in strips from the three rat types. It was found that carbachol and 5-HT elicited tracheal contraction in a si milar manner in strips from the three types of rats. Histamine had no contr actile effect. Compound 48/80, at a dose of 25 mu g/ml, elicited contractio n in tracheas from both control (+/+) and heterozygous (Ws/+), but not in t rachea from Ws/Ws rats. Compound 48/80-induced contractions in tracheas fro m +/+ rats were inhibited by 0.1 mu M ketanserin and 0.1 mu M nedocromil, b ut not by 0.1 mu M mepyramine. Enzyme histochemistry confirmed that the deg ranulation occurred in connective tissue mast cells, but not in mucosal mas t cells. We concluded that connective tissue mast cells play an important r ole in rat tracheal contraction via 5-HT release induced by compound 48/80. In addition, the specific mast cell-deficient (Ws/Ws) rats provide a good tool for studying the roles of mast cells in airway system. (C) 2000 Elsevi er Science B.V. All rights reserved.