Intravitreal l-Arginine injection reverses the retinal arteriolar vasoconstriction that occurs after experimental acute branch retinal vein occlusion

To investigate the effect of l-Arginine on the retinal arteriolar diameter following acute branch retinal vein occlusion (BRVO) in minipigs. Under general anesthesia, 10 eyes of 10 minipigs were evaluated. Two hours after BRVO, an intravitreal juxta-arteriolar micro-injection of 30 μl l-Arginine 1 mM (pH = 7.4) was performed in 7 eyes. Three eyes received a micro-injection of 30 μl of the solvent (pH = 7.4) that was used to prepare the solution of l-Arginine and served as controls. Retinal arteriolar diameter changes were measured using a Retinal Vessel Analyzer. Overall (n = 10), 2 h after BRVO there was a 10.5 ± 1.9% decrease in the retinal arteriolar diameter in the affected territories compared to baseline (p < 0.001). An increase of 16.0 ± 3.0% (p = 0.001) and 21.0 ± 7.0% (p = 0.013) of the arteriolar diameter was evidenced 10 and 15 min respectively after l-Arginine injection (n = 7) compared to the diameter prior to l-Arginine injection. Thereafter, the vasodilatory effect of l-Arginine started to decrease but persisted and remained significant at the end of the study period (5.0 ± 1.5% at 30 min, p = 0.007). Micro-injection of the solvent alone (n = 3) did not produce any significant effect on the retinal arterioles, which remained constricted at all time-points (p > 0.1). These findings demonstrate a significant arteriolar vasodilation after intravitreal juxta-arteriolar l-Arginine micro-injection in eyes with experimental BRVO in the affected territories. l-Arginine micro-injection can reverse the arteriolar vasoconstriction that occurs in acute experimental BRVO by stimulating nitric oxide production.