Endothelin-1 attenuates increases in hydraulic conductivity due to platelet-activating factor via prostacyclin release

Abstract

We previously showed that endothelin-1 (ET-1) and prostacyclin (PGI2) similarly attenuate increases in microvascular permeability induced by platelet-activating factor (PAF). This led us to hypothesize that ET-1 attenuates trans-endothelial fluid flux during PAF through PGI2release. We tested this hypothesis in three phases. First, bovine pulmonary artery endothelial cells were exposed to 0.008–8 μM ET-1 and assayed for PGI2release. Second, to determine whether increased transmonolayer flux after PAF could be attenuated by ET-1 or PGI2and reversed by PGI2synthesis inhibition or PGI2receptor blockade, we measured endothelial cell transmonolayer flux after cells were exposed to 10 nM PAF plus 10 μM PGI2or 80 pM ET-1, with or without 500 μM tranylcypromine (PGI2synthase inhibitor) or 20 μM CAY-10441 (PGI2receptor blocker). Finally, hydraulic conductivity (Lp) was measured in rat mesenteric venules in vivo after exposure to 10 nM PAF and 80 pM ET-1 with or without tranylcypromine (100 and 500 μM) or CAY-10441 (2 and 20 μM). We found that in vitro, ET-1 stimulated a dose-dependent increase in PGI2production (from 126 to 217 pg/ml, P < 0.01). Compared with PAF alone, PGI2plus PAF and ET-1 plus PAF decreased transmonolayer flux similarly by 52 and 46%, respectively ( P < 0.01), while tranylcypromine and CAY-10441 reversed these effects by 92 and 47%, respectively ( P < 0.05). In vivo, PAF increased Lpfourfold ( P < 0.01) and ET-1 attenuated this effect by 83% ( P < 0.01). Tranylcypromine and CAY-10441 reversed the ET-1 attenuation in Lpduring PAF by 55 and 45%, respectively ( P < 0.01). We conclude that ET-1 may stimulate endothelial cell PGI2release to attenuate the increases in transmonolayer flux and hydraulic conductivity secondary to PAF.