Changes in the pattern of distribution of von Willebrand factor in rat aortic endothelial cells following thrombin generation in vivo

The pattern of distribution of von Willebrand factor (VWF) in relatively large sheets of rat aortic endothelial cells (EC) obtained by the Häutchen technique were analysed by immunocytochemistry and light microscopy. EC were examined pre and post administration of a procoagulant mixture of factor Xa (F.Xa) and phosphotidylcholine/phosphotidylserine (PCPS) vesicles which was demonstrated to result in the selective loss of high molecular weight multimers (HMWM) of plasma VWF in the rat. In placebo animals the pattern was heterogenous both in overall distribution and in individual cells which showed both a diffuse and granular pattern. Groups of intensely stained EC were oriented parallel to the longitudinal axis of the aorta and staining was particularly prominent around the orifices of the intercostal arteries, implicating shear-stress as a possible factor in VWF expression by EC. Changes in the pattern of distribution of staining were observed at various time points post-infusion of F.Xa/PCPS, suggesting the immediate release of VWF from EC stores followed by the recruitment of EC to synthesize and store VWF. These changes are consistent with the decrease in EC Weibel-Palade Body (WPB) content observed by EM in previously reported studies using this model.