PURPOSE. To investigate the regulation of an adenosine agonist, 2-5’-N-ethylcarboxamidoadenosine (NECA) on the outward active transport of fluorescein across rabbit blood retinal barrier (BRB).METHODS. Pigmented rabbits were given an intravitreous injection of various concentrartions of NECA or phosphate buffered saline (PBS). Sodium fluorescein was intravenously injected 180 minutes after NECA injection. Differential vitreous fluorophotometry (DVF) was performed 180 minutes after intravenous injection of sodium fluorescein to measure fluorescein (F) and fluorescein monoglucuronide (FG) concentrations in the vitreous. The F/FG ratio was calculated as an indicator of the estimated outward active transport of the BRB. Retinal detachments were experimentally produced by injection of PBS into the subretinal space. Experimental solution or PBS were injected intravitreally, and the size of blebs was monitored under masked conditions.RESULTS. In eyes with intravitreal injection of high dose NECA, F/FG ratio was significantly lower when compared with in controls (p<0.05), but in eyes with low dose injection that was higher (p<0.05). The effect of high dose NECA on F/FG ratio was suppressed by the A1 receptor antagonist, 8-cyclopentyl-1, 3-dipropylxanthine (CPX) and the effect of low dose NECA was suppressed by the A2 receptor antagonist, ZM241385. The A3 receptor antagonist MRS1191 didn’t have an influence on the effect of high or low dose NECA. Intravitrteal injection of high dose NECA enhanced the removal of subretinal fluid when compared with intravitrteal injection of PBS alone. CONCLUSIONS. These data suggest that intravitreous injection of high dose NECA accelerate the active outward transport of the BRB via A1 receptors and low dose NECA decelerate it via A2 receptors, and A3 receptors don’t contribute to the regulation of it.
