Effect of Adenosine on Outward Active Transport of Fluorescein across Rabbit Blood Retinal Barrier

Abstract

Abstract: : Purpose:To investigate the effect of adenosine on outward active transport of fluorescein across rabbit blood retinal barrier using differential vitreous fluorophotometry (DVF). Methods: New Zealand white rabbits about 2.5kg were injected intravitreously with the nonselective adenosine receptor agonist 2-5’-N-ethylcarboxamidoadenosine (NECA) at concentrations from 1x10^-5M to 2x10^-3M in 0.1ml or 0.1ml of phosphate buffer saline (PBS) alone. Sodium fluorescein was injected intravenously 180 minutes after the intravitreous injection. DVF was performed 180 minutes after intravenous injection of sodium fluorescein. The vitreous concentrations of fluorescein (F) and fluorescein monoglucuronide (FG) were measured, and the F/FG ratio was calculated as an index of outward active transport of blood retinal barrier (BRB). Results:At concentrations of NECA from 1x10^-5M to 2.5x10^-4M, the F/FG ratio was significantly higher than that of controls (p<0.05), which was inhibited by the A2-selective antagonist ZM241385. On the contrary, at concentrations from 5x10^-4M to 2x10^-3M, the F/FG ratio was significantly smaller (p<0.05) when compared that of controls, which was inhibited by the A1-selective antagonist 8-cyclopentyl-1,3-dipropylxanthine (CPX).The A3-selective antagonist MRS1191 didn’t inhibit the effect of NECA on outward active transport of BRB. Conclusions:This study showed that low-dose adenosine inhibited outward active transport of BRB via A2-receptors, high-dose adenosine accelerated it via A1-receptors, and A3-receptors didn’t contribute to the regulation of active transport of BRB.

Keywords: adenosine • retinal pigment epithelium • vitreous