Perilla ketone (PK) is a potent lung toxin that causes increased microvascular permeability pulmonary edema in grazing animals. Because the mechanism of action of PK is not know, we investigated whether PK directly affects endothelial cells. Bovine aortic endothelial cells were grown to confluence on Cytodex-3 microcarrier beads and placed in a chromatographic cell column. Monolayer permeability was evaluated from the elution profiles of three optical tracers: blue dextran (2 x 10(6) mol wt), sodium fluorescein (NaF, 342 mol wt), and cyanocobalamin (B12, 1,355 mol wt). Perfusion with 1.2 mM PK increased permeability within 15 min to NaF and B12 by 51 +/- 6 and 54 +/- 11%, respectively. Permeability returned to baseline after PK removal. These in vitro results suggest that PK produces a rapid and reversible increase in endothelial permeability directly. Staining of fixed cells with rhodamine-phalloidin revealed a major disruption of actin microfilaments after PK treatment. Because previous reports suggested that PK may be activated via cytochrome P-450, we attempted to block this using the cytochrome P-450 inhibitor ketoconazole. Ketoconazole alone did not significantly affect permeability, and the combination of PK and ketoconazole resulted in permeability increases similar to those measured for PK alone. This suggests that PK may not require cytochrome P-450 to increase vascular permeability.