Effect of nucleotide P2Y2 receptor agonists on outward active transport of fluorescein across normal blood-retina barrier in rabbit

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Background. To evaluate the effect of nucleotide P2Y2 receptor agonists INS542 and uridine 5′-triphosphate (UTP) on the outward active transport of fluorescein across rabbit blood-retina barrier (BRB) in vivo.Methods. Injection (0·1 ml) of INS542 (0·1 or 1 mm), phosphate buffered solution, or UTP (1 or 10 mm) was made in Dutch-belted rabbits. Differential vitreous fluorophotometry (DVF) was performed 3 hr later and the fluorescein (F)/fluorescein monoglucuronide (FG) ratio was then calculated. F/FG ratios are inversely proportional to outward active transport of F across BRB at the level of the retinal pigment epithelium (RPE). In another set of experiments, the effect of 0·1 ml vitreous injection of INS542 (1 mm) on F/FG ratios was evaluated at different time points ranging from 0·5 to 48 hr before conducting DVF.Results. F/FG ratios obtained 3 hr after intravitreal injection were as follows (mean±standard error): 0·49±0·14 (0·1 mm INS542), 0·19±0·04 (1 mm INS542), 0·48±0·09 (PBS), 0·40±0·08 (1 mm UTP) and 0·36±0·05 (10 mm UTP). The F/FG ratio for 1 mm INS542 was significantly lower than in the other groups (P<0·05). In the time course experiments, a significant decrease in the F/FG ratios was observed between 1 and 12 hr following administration of INS542 when compared with F/FG ratios obtained in the contralateral (untreated) eye.Conclusion. Intravitreal administration of INS542 (but not UTP) enhances outward active transport of F across RPE in intact rabbit eye, indicating that activation of P2Y2 receptors in vivo directly stimulates RPE active transport.

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