Neuropeptide Y enhances permeability across a rat aortic endothelial cell monolayer

Previously, in vivo studies showed that neuropeptide Y (NPY) elevates vascular permeability in isolated lung perfusion preparations, possibly through binding to the NPY Y₃ receptor. The present study used monolayers in a double-chamber culture method under conditions of normoxia (5% CO ₂-20% O₂-75% N₂) or hypoxia (5% CO ₂-5% O₂-90% N₂) to test the hypothesis that NPY directly affects rat aortic endothelial cells (RAECs). RAECs were cultured on the base of the upper chamber, into which FITC-labeled albumin was introduced, and permeation into the lower chamber was measured. The RAEC monolayer was treated with 10^-8-3 × 10^-7 M NPY for 2 h in normoxia or hypoxia. In hypoxia, NPY concentration dependently increased the permeability of the RAEC monolayer, whereas in normoxia no significant change was observed. Peptide YY, NPY Y₁, and NPY Y₂ receptor agonists and NPY Y₁ receptor antagonist exerted no significant effects under hypoxic conditions. NPY-(18-36), an NPY Y₃ receptor antagonist, elicited an inhibitory action on the NPY-induced increase in monolayer permeability. Furthermore, neither N-mono-methyl-L-arginine, a nitric oxide synthase inhibitor, the bradykinin B₂ receptor antagonist FK-3657, nor the vascular endothelial growth factor receptor-coupled tyrosine kinase inhibitor tyrphostin SU-1498, injected into the medium of the upper chamber, affected the NPY-induced permeability changes under hypoxic conditions. The results suggest that the NPY-induced increase in permeability across the RAEC monolayer is closely related to low O₂ tension, possibly mediated by direct action on the NPY Y₃ receptor expressed on the endothelial cell membrane. Furthermore, this NPY-induced increase is not likely due to nitric oxide, bradykinin, or vascular endothelial growth factor.