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% CO2-20% O2-75% N2) or hypoxia (5% CO2-5% 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-monomethyl-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.
Effects of Vascular Endothelial Growth Factor on the Lymphocyte-Endothelium Interactions: Identification of Caveolin-1 and Nitric Oxide as Control Points of Endothelial Cell Anergy