Effect of CO2 induced pH changes on the response of isolated guinea pig tracheas to theophylline

The effect of CO2 induced pH changes on the response of airway smooth muscle to theophylline was studied. Our data show that simulated respiratory acid-base disturbances (pH range 7.0 to 7.8) have no significant effect on the response of isolated guinea pig tracheal cylinders at basal tone to theophylline. On the other hand, tracheal cylinders precontracted with histamine showed a diminished sensitivity to theophylline at pH values above 7.40, and an enhanced sensitivity at pH values below 7.40.