The functional integrity of the blood-retinal barrier (BRB) is crucial for proper vision. The BRB consists of inner and outer components composed by vascular endothelium and retinal pigment epithelial (RPE) cells, respectively. We recently showed that the hormone prolactin (PRL) acts as an endogenous retinal trophic factor able to limit retinal degeneration [1]. In addition to regulating glial-neuronal cell interactions, we postulated that PRL targets RPE cells. Adding complexity to PRL actions is its structural polymorphism. In the retina, PRL is proteolytically cleaved to vasoinhibins [2] that prevent the excessive retinal vasopermeability associated with diabetes [3]. However, whether vasoinhibins act on the RPE component of the BRB is unknown. BRB permeability was quantified by the Evans blue method in male Wistar rats. Rats were anesthetized with ketamine (60 mg/kg) and xylazine (25 mg/kg, both I.M.). Adult human RPE cell-line (ARPE-19) monolayers were assessed for transepithelial electrical resistance. We found that RPE in transverse sections of rat retinas express the PRL receptor mRNA and protein by in situ hybridization and immunochemistry, respectively. PRL receptor was also detected in ARPE-19 cell monolayers. PRL induced a transient increase in the resistance of ARPE-19 monolayers that peaked at 30 minutes. On the other hand, we tested if vasoinhibins attenuate the breakdown of BRB induced by the intravitreal injection of bradykinin (BK), a main effector of the kallikrein-kinin system contributing to the BRB breakdown associated with diabetes. Intravitreal injection of BK in rats under anaesthesia (as dose and route previously provided) enhanced BRB breakdown compared to saline, but co-injection with vasoinhibins prevented this effect, as did the BK B2 receptor antagonist Hoe-140. Also, vasoinhibins prevented the transient decrease in ARPE-19 cell monolayer resistance induced by BK. Notably, the antioxidant N-acetyl cysteine and vasoinhibins blocked the action of BK and of the radical initiator Luperox, respectively, on ARPE-19 monolayer resistance. BK promoted intracellular ROS formation in ARPE-19 cells, an effect that was prevented by vasoinhibins. Finally, we observed that the intravitreal injection of vasoinhibins reduced the retinal levels of ROS in streptozotocin-induced diabetic rats (I.P. for 4 weeks) compared with controls. These data show that the PRL/vasoinhibin team maintains the functional integrity of the outer BRB by limiting retinal oxidative stress, thus offering potential treatment strategies against diabetes-related retinopathies.