Hyperventilation-induced airway injury and vascular leakage in dogs: Effects of α₁-adrenergic agonists

α₁-Adrenergic agonists inhibit hyperventilation-induced bronchoconstriction (HIB) in dogs. We tested the hypothesis that α-agonists inhibit HIB by reducing bronchovascular leakage and edema that theoretically could cause airway obstruction. Peripheral airways were isolated by using a bronchoscope; pretreated with either methoxamine (Mx), norepinephrine (NE), or saline aerosol; and then exposed to a 2,000 ml/min dry-air challenge (DAC) for 2 min. Colloidal carbon was injected before DAC and used to quantify bronchovascular permeability. Mx-, NE-, and vehicle-treated airways were prepared for morphometric analysis within 1 h after DAC. Light microscopy revealed that the 2-min DAC produced minimal bronchovascular leakage and little epithelial damage. However, pretreatment with either Mx or NE significantly enhanced dry air-induced bronchovascular hyperpermeability and mucosal injury. The increased damage associated with these α₁-agonists implicates a protective role for the bronchial circulation. The fact that α₁-agonists inhibit HIB suggests that neither dry air-induced leakage nor injury directly contributes to the development of airway obstruction. In addition, our data suggest that α-agonists attenuate HIB in part by augmenting hyperventilation-induced bronchovascular leakage and by replacing airway water lost during a DAC.