Retinal vascular changes in rats with inherited hypercholesterolemia - Corrosion cast demonstration

Purpose. To demonstrate specific hypercholesterolemic changes in the retina l vascular architecture. Methods. Corrosion casts of 12- to 18-month-old rats with inherited hyperch olesterolemia (RICO) and of control Wistar Kyoto (WKy) rats were examined w ith a scanning electron microscope (SEM). The diameters of the retinal arte ries, veins and capillaries were measured in photographs with a caliber mic rometer. The capillary branches were counted in the micrographs with the us e of Adobe Photoshop. The retinal capillaries were examined by transmission electron microscopy (TEM). Results. SEM examination of the vascular casts of 15-month-old RICO rats sh owed slight tortuosity of large vessels at the posterior pole of the retina . The precapillary arterioles branching from the major artery were longer a nd straighter than normal. Retinal capillary changes such as caliber irregu larity and narrowing in the capillary network were more severe in 18-month- old RICO rats. The most prominent finding was marked straightening of the c apillaries in the inner and outer layers of the capillary network, which lo oked like fine strings. Intercapillary spaces became wider, and finally cap illaries looked scattered. The diameter of the retinal capillaries lumen in RICO rats was significantly narrower than that in WKy rats (p < 0.0001). T he capillary branches were fewer in 18-month-old RICO rats than that in 18- month-old WKy rats (p < 0.0001). Neither local stenosis or obstruction in t he arterioles and venules nor any arteriovenous crossing defect was seen in young and old RICO rats. Transmission electron microscopy of 16-month-old RICO rat retinas revealed that the capillaries in the inner and outer plexi form layers contained scarce cytoplasmic components, vacuoles in endothelia l cells and basement membranes of irregular thickness. Capillary pericytes were swollen and irregular in shape, contained vacuolated mitochondria and scarce cytoplasmic components. Conclusions. These findings indicate that the retinal capillary changes are probably related to hypercholesterolemia.