Effect of Antiasthma Drugs on Microvascular Leakage in Guinea Pig Airways

We have studied the effect of intravenous epinephrine, albuterol, verapamil, and aminophylline on airway microvascular leakage in guinea pigs. Microvascular leakage was induced by platelet-activating factor (PAF; 50 ng/kg intravenously), which acts directly on venular endothelial cells, and measured by quantifying extravasation of Evans blue (EB) dye. Epinephrine (20 µg/kg) inhibited PAF-induced changes in dye leakage in larynx and main bronchi; at 80 and 160 µg/kg, significant inhibition was observed in all airways studied. This effect was reversed by phentolamine (2.5 mg/kg) or prazosin (100 µg/kg). By contrast, albuterol (20 to 320 µg/kg) and aminophylline (12.5 to 50 mg/kg) failed to inhibit dye leakage at any dose studied. Verapamil inhibited PAF-increased leakage in larynx, main bronchi, and intrapulmonary airways at the lowest dose tested (125 µg/kg), although inhibition was not dose dependent. These results suggest that the antiedema effect of epinephrine may be due to vasoconstriction rather than to a direct effect on endothelial cell contractility and that neither β-agonists nor theophylline have an inhibitory effect. The inhibitory effect of epinephrine on airway microvascular leakage may have therapeutic implications for asthma.