HETEROGENEOUS ENDOTHELIAL-CELL STRUCTURE ALONG THE PORCINE RETINAL MICROVASCULATURE

The pivotal role of the endothelial cell in the regulation of Vascular tone has been well demonstrated in many vascular beds, including the retina. However, in the retina, little is known about how the structur al elements of the endothelial cells are arranged along the arborisati on pathway from artery to vein, the nature of which has been linked to functional heterogeneity in other vascular beds. The relative vulnera bility of the retina to vascular based diseases, and the heavy relianc e on local regulation of the retinal vasculature makes an improved und erstanding of such local regulatory mechanisms of significant clinical importance. The present study focuses on identifying differences in e ndothelial cells along the arborisation pathway in the porcine retinal vasculature. Enucleated pig eyes were arterially cannulated and perfu sed with fixative followed by double staining for F-actin microfilamen ts (rhodamine phalloidin) and nucleic acid (YO-PRO-1). The intact reti na was then viewed by confocal microscopy. The distribution of F-actin , Vessel diameter, endothelial cell size and shape, nucleus size and s hape, and position within the cell were determined as a function of lo cation along the vascular tree. The main retinal arterioles (A(1)) con tained full length F-actin internal stress fibers which lay parallel t o the long axis of the endothelial cell. Subsequent branches from the A(1) arteriole (A(2) and A(3)) showed fewer, shorter fibers, with none visible in the A(4) and A(5) branches, the capillaries, or in the ven ous side of the vasculature. All endothelial cells showed peripheral b order staining of F-actin microfilaments which allowed the shape of th e cell to be determined. All endothelial cells were elongated with the long axis parallel to the vessel, but the mean aspect ratio decreased from 10.9+/-0.5, S.E.M. in the A(1) arterioles to 3.2+/-0.2 in the ma jor Veins (V-1). The position of the endothelial cell nucleus relative to the cell was eccentric in the downstream direction in the A(2)-A(5 ) arterioles, whilst centrally placed in the A(1) arterioles and veins . The structural heterogeneity of endothelial cells along the pig reti nal circulation suggests that functional heterogeneity of the endothel ium may be involved in regulation of retinal blood now. (C) 1997 Acade mic Press Limited.