HYPOXIA INDUCES PMN ADHERENCE TO UMBILICAL VEIN ENDOTHELIUM

Objective: In vitro incubation of cultured endothelial cells under hyp oxia leads to the activation of these cells and results in an increase of their adhesiveness for neutrophils (PMN). Because of the possible relevance of these observations for pathological situations, we invest igated whether adherence of PMN also occurs in an entire vein after it s incubation in hypoxic conditions. Methods: Human umbilical veins in complete cords were incubated for 2 h in normoxic or hypoxic condition s and the adherence of unstimulated human Cr-51-labelled-PMN was measu red under flow conditions. Experiments with human umbilical vein endot helial cells (HUVEC) were performed in parallel for comparison. Morpho logical studies in scanning electron microscopy were carried out in bo th in vitro and ex vivo situations. Results: Hypoxia induced an increa se in the adherence of PMN either to HUVEC or to the umbilical vein en dothelium up to 5- to 6-fold when compared to normoxic conditions (P < 0.001). In both cases, this hypoxia-induced adherence was inhibited b y anti-ICAM-1 antibodies or when the PAF (platelet-activating factor) synthesis was blocked during hypoxia by oleic acid, Furthermore, the a dherence of PMN was inhibited when PMN were pre-incubated with WEB 208 6 (a selective PAF receptor antagonist). These results indicate a cruc ial role of PAF in this process. Morphological studies confirmed that the number of PMN adherent to hypoxic HUVEC or to the hypoxic umbilica l vein endothelium was much greater than the number of PMN on normoxic endothelial cells. Both in vitro and ex vivo, PMN adherent to the hyp oxic endothelial cells to the contrary of the ones adherent to normoxi c endothelial cells demonstrated membrane foldings typical of an activ ated state. Conclusion: These results show that in a complete vein, hy poxia induced an increased adhesiveness of endothelial cells for PMN b y a similar mechanism to the one observed for cultured endothelial cel ls. They suggest an active role of endothelial cells in the initiation of the inflammatory response often described in ischemic-reperfused o rgans.