It has been found that rat choriocapillaris had 50 percent fewer pericytes than retinal capillaries. Also, unlike retinal capillaries, pericyte loss does not occur in rat experimental diabetes. Choriocapillaris is unique in that only the retinal side of the capillary has fenestrae, making transport of nutrients to RPE and photoreceptors and removing waste from photoreceptor disk shedding and RPE digestion of these disks more efficient. The same sidedness is observed in the location of VEGF receptors. It has been reported that both VEGF receptor-1 (FLT-1) and VEGF receptor 2 (FLK-1 or KDR) are found on endothelial cells on the retinal side of the choriocapillaris. Perhaps this is related to the basal production of VEGF by RPE. RPE was actually one of the first cells shown to produce VEGF and upregulate production during hypoxia. Perhaps the release of VEGF on the retinal side encourages maintenance of fenestrae on the retinal side of the choriocapillaris.
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