Effect of Dexamethasone on Endothelial Extracellular Matrix Formation and on Its Reactivity to Platelets in a Perfusion System

Abstract

We previously demonstrated that dexamethasone increases fibronectin (FN) expression by human umbilical vein endothelial cell (HUVEC) as well as its incorporation in the extracellular matrix (EM). FN is primarily involved in platelet/vessel wall interactions as well as in cell attachment to substrates. The in vivo anti-haemorragic effect of glucocorticoids could therefore be related either to a better spreading and attachment of endothelial monolayer to the basement membrane or to an increase of vessel wall reactivity to platelets. To further investigate this, we studied the effect of dexamethasone treatment on EM reactivity to platelets in an in vitro perfusion system. Second passage HUVEC were seeded on glass coverslips at a density of 105/cm2 and treated with dexamethasone 1.0 μM for 48 hours. EM were prepared by exposure to 0.1 M NH4OH for 30’. Coverslips carrying the EM were perfused with citrated whole blood in a flat perfusion chamber(*) at wall shear rates of 300 and 900 sec™1 for 5’. Platelet adhesion to EM was evaluated by a morphometric method. The number of platelet adhering to EM at both shear rates was significantly increased by dexamethasone treatment, (+51.9% at 300 sec™1 (p<0.001) and +24.3% at 900 sec™1 (p<0.01)). Our results demonstrate that dexamethasone increases endothelial EM reactivity to platelets possibly through an increase of FN deposition. This, together with FN effect on cell spreading and anchorage to EM, might be responsible for the antl-haemorrhagic action of glucocorticoids.(*) K. Sakanassen et al . , J . Lab. Cl in . Med. 102:522, 1983