CALCIUM CHELATORS INCREASE AIRWAY RESPONSIVENESS

To test the effect of Ca chelation on airway responsiveness to methacholine, purebred Basenji dogs were pretreated with a Ca chelating aerosol (edetate disodium, Na2EDTA) or a placebo aerosol (saline or CaNa2-EDTA) and then challenged with methacholine bromide aerosols. The lowest dose of methacholine (0.15 mg/ml) produced no change in pulmonary resistance (RL) following pretreatment with the placebo aerosols, but RL increased (P < 0.05) by 5.1 .+-. 1.2 (SE) cmH2O .cntdot. l-1.cntdot. s following pretreatment with Na2EDTA. The highest dose of methacholine (1.5 mg/ml) increased RL in all animals, but the increase was greater (P < 0.01) following pretreatment with Na2EDTA (9.5 .+-. 1.9 cm H2O .cntdot. l-1 .cntdot. s) than following pretreatment with a placebo aerosol (6.4 .+-. 1.5 cmH2O .cntdot. l-1 .cntdot. s). Ca-chelating aerosols significantly increase airway responsiveness and suggest that a localized Ca deficit may contribute to hyperresponsive airway disease.