In vivo evaluation of platelet-endothelial interactions in retinal microcirculation of rats.

Purpose: This study was designed to develop a new method to evaluate the dynamics of platelets in the retinal microcirculation in vivo and to investigate quantitatively the platelet-endothelial interactions in rat retina with the use of this system.
Methods: Isolated platelet samples were labeled with carboxyfluorescein diacetate succinimidyl ester. After intravenous administration, platelet behavior in the retinal microcirculation was evaluated with a scanning laser ophthalmoscope. The images were recorded on S-VHS videotape and analyzed with a computer-assisted image analysis system. The platelet- endothelial interactions in the retinal microcirculation were also investigated with the use of lipopolysaccharide-stimulated endothelium or platelets activated with thrombin.
Results: Fluorescent platelets were recognized as distinct dots in the retinal microcirculation and could be traced frame by frame. The velocity of platelets in the retinal arteries, capillaries, and veins was 26.1+/-6.4, 1.6+/-0.4, and 19.9+/-8.2 mm/sec, respectively. In control rats, even the activated platelets showed minimal interaction with retinal endothelial cells. In contrast, stimulated retinal endothelium showed active platelet- endothelial interactions; many platelets were observed rolling and adhering along the major retinal veins. The interactions between platelets and stimulated endothelial cells were substantially inhibited with the injection of P-selectin monoclonal antibody.
Conclusions: The present study demonstrated a new method to visualize platelet behavior in the retinal microcirculation in vivo. This method will allow quantitative evaluation of platelet dynamics and platelet- endothelial interactions in retinal pathologic conditions.