Hyperthyroidism protects against carbachol-induced bronchospasm.

We studied the effect of increased thyroid function on airway reactivity. Carbachol challenge was performed to assess airway reactivity according to a standardized method. Measurements of forced expiratory volume-1 second (FEV1), specific airway conductance (SGaw), the provocative dose of carbachol for a 20 percent decrease in FEV1 (PD-20) and that for a 35 percent decrease in SGaw (PD-35) were established upon entry when each subject was hyperthyroid, and subsequently, after the subjects had returned to the euthyroid state. It was concluded that hyperthyroidism reduced the severity of carbachol-induced changes in airway reactivity as measured by SGaw.