The responses of choriocapillary endothelial cells（CCE） and retinal capillary endothelial cells（RCE） in culture

in terms of phosphoinositide（PI） breakdown and cellular mitogenesis

to retinal pigment epithelial cell（RPE）-conditioned medium and vasoactive agents have been compared. RPE-conditioned medium did not induce PI breakdown in either type of cell. However

it stimulated DNA synthesis in CCE but not in RCE. Bradykinin（BDK） acted as both a fast signaling and a slow mitogenic factor on CCE

but BDK did not affect PI turnover or DNA synthesis in RCE. In contrast

thrombin stimulated PI turnover in RCE but not in CCE

though it did not induce 3H-thymidine incorporation into either type of cell. These differences in cellular functions between CCE and RCE following stimulation suggest that induction of DNA synthesis and receptor-mediated PI turnover by external factors is determined

at least in part

by the origin of the capillary endothelial cell. Therefore

extrapolation to CCE pathophysiology from experiments using endothelial cells from other capillary origins may not be valid.