Objective:In this study, we evaluated the spasmolytic effect of intravenous prostaglandin (PG) E1on histamine-induced bronchoconstriction with a direct visualization method using a superfine fiberoptic bronchoscope.Setting:A university research laboratory.Subjects:Mongrel dogs.Interventions:The bronchial cross-sectional area (BCA) of mongrel dogs was measured by a direct visualization method using a superfine fiberoptic bronchoscope. Bronchoconstriction was elicited with histamine (H) infusion: 10 μg/kg iv bolus + 500 μg/kg/h continuous iv. The first protocol (n = 7) was designed to determine the effects of intravenous bolus of PGE1: 0 (saline), 0.01, 0.1, 1.0 and 10 μg/kg on H-induced bronchoconstriction. BCA was assessed before and 30 min after starting the H infusion and 5 min after each dose of intravenous PGE1. The second protocol was designed to determine whether continuous intravenous infusion of PGE1reverses H-induced bronchoconstriction. In the PG group (n = 6), PGE1was continuously infused at 0.1 μg/kg/min (20 mL/hr). In the control group (n = 6), saline was administered at a rate of 20 mL/hr iv. BCA was assessed before and 30 min after starting the H-infusion and at 5, 10, 30 and 60 min after commencing the PGE1or saline infusion. Arterial blood was obtained simultaneously for measurement of plasma concentrations of epinephrine and norepinephrine by gas chromatography mass spectrometry.Measurements and Main Results:In the first protocol, PGE1produced a dose-dependent increase in the percentage of BCA and 10 μg/kg of PGE1almost fully reversed the H-induced bronchoconstriction. Plasma catecholamines did not change significantly. In the second protocol, continuous infusion of PGE1produced a time-dependent reversal of H-induced bronchoconstriction (percentage of BCA increased to 80.0 ± 9.0% 60 min after the start of PGE1infusion), whereas saline infusion did not reverse the bronchoconstriction. Plasma catecholamines did not change significantly in either group.Conclusions:Both intravenous bolus and continuous intravenous infusion of PGE1reversed the H-induced bronchoconstriction. PGE1may be used safely for patients with the hyperreactive airway and might be useful as a therapeutic agent for these patients.