Response of bronchial smooth muscle to mast cell degranulation in situ

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Abstract
The response of bronchial smooth muscle to mast cell degranulation with Ascaris suum antigen (AA) and compound 48/80 (48/80) was studied in 26 mongrel dogs in situ. Bronchial smooth muscle response was measured isometrically in situ from a segment of the right middle lobe bronchus; tracheal response was monitored isometrically as a control. After intra-arterial (ia) injection of AA into the bronchial circulation, bronchial contraction preceded tracheal contraction by 19.2 .+-. 4.6 s (P < 0.002). Bronchial contraction to AA (21.7 .+-. 3.4 g) was substantially greater than to 48/80 (10.5 .+-. 1.8 g, P < 0.05) corresponding to differences in maximal systemic histamine concentrations (146 .+-. 24.1 vs. 1000 .+-. 236 ng/ml, P < 0.01). In 5 dogs, the effect of leukotriene D4 (LTD4) and FPL 55712 was studied. Injection of 10-8 mol ia LTD4 caused no bronchial contraction. In 4 dogs, 10-7 mol FPL 55712 caused no bronchial relaxation after initial precontraction during immune degranulation with AA; i.v. chlorpheniramine (5 mg/kg) caused 69.7 .+-. 9.4% relaxation. A model that permits selective immune degranulation of a single major resistance bronchus in situ was demonstrated. AA-induced degranulation in dogs causes bronchial contraction predominantly by secretion of preformed mediator.

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