HYPERPERMEABILITY OF PULMONARY ENDOTHELIAL MONOLAYER - PROTECTIVE ROLE OF PHOSPHODIESTERASE ISOENZYME-3 AND ISOENZYME-4

The regulation of endothelial permeability is poorly understood. An in crease in endothelial permeability in the pulmonary microvasculature, however, is critical in noncardiogenic pulmonary edema and other diffu se inflammatory reactions. In the present study thrombin and Escherich ia coli hemolysin (HlyA), a membrane-perturbing bacterial exotoxin, we re used to alter hydraulic permeability of porcine pulmonary artery an d human endothelial cell monolayers. We also investigated the pharmaco logical approach of adenylyl cyclase activation/phosphodiesterase (PDE ) inhibition to block endothelial hyperpermeability. Thrombin (1-5 uni ts/ml) and HlyA (0.5-3 hemolytic units/ml) dose and time dependently ( >15 min) increased endothelial permeability. Forskolin, cholera toxin, and prostaglandin E(1), which all stimulate adenylyl cyclase activity , abrogated this effect. One mM dibutyryl cAMP, a cell membrane-permea ble cAMP analogue, was similarly active. Endothelial hyperpermeability was also reduced dose dependently by inhibitors of different PDE isoe nzymes (motapizone, rolipram, and zardaverine, which block PDE3 and/or PDE4). The effectiveness of PDE inhibitors was increased in the prese nce of adenylyl cyclase activators. Analysis of cyclic nucleotide hydr olyzing PDE activity in lysates of human umbilical vein endothelial ce lls showed high activities of PDE isoenzymes 2, 3, and 4. Consistent w ith the functional data PDE3 and PDE4 were the major cAMP hydrolysis e nzymes in intact endothelial cells. We conclude that the hyperpermeabi lity of pulmonary endothelial monolayers, evoked by thrombin or HlyA, can be blocked by the simultaneous activation of adenylyl cyclase and inhibition of PDEs, especially of PDE3 and PDE4. The demonstration of PDE isoenzymes 2-4 in human endothelial cells will help optimize this therapeutic approach.