The vasodilatory effect of juxta‐arteriolar microinjection of endothelin‐A receptor inhibitor in healthy and in acute branch retinal vein Occlusion Minipig Retinae

Abstract Purpose: To investigate the vasoactive effect of endothelin‐A receptor inhibitor BQ‐123 on the retinal arteriolar vasculature in normal and in acute branch retinal vein occlusion (BRVO) minipig retinae. Methods: Under general anesthesia, 6 normal eyes of 6 minipigs and 5 eyes of 5 minipigs with acute experimental BRVO were evaluated. In all eyes, a slow, continuous microinjection of 30 μl BQ‐123 (0.67 μg/ml) was performed 50 to 100 μm away from a retinal arteriole, avoiding exerting pressure on retina’s anatomic structures. After the microinjection, the retinae were observed for changes in vessels’ diameter. The procedure was recorded in real time. Throughout the procedure, the animals’ vital signs were monitored. Results: Overall (n=11), an increase of 18.56% and 26.45% in arteriolar diameter was evidenced 5 and 15 minutes respectively after BQ‐123 microinjection. When separately examining normal (n=6) versus OBVR (n=5) eyes, the increase in arteriolar diameter 5 minutes post injection was 16.75% versus 19.86% respectively (P=0.491), whereas the increase in arteriolar diameter 15 minutes post injection was 25.14% versus 27.4% (P=0.591). Conclusions: Our results demonstrate a significant increase in retinal arteriolar diameter after juxta‐arteriolar BQ‐123 microinjection, both in healthy and in acute OBVR retinae. There was no statistically significant difference between the amount of vasodilation exerted by BQ‐123 on healthy and on BRVO retinae. This vasodilatory effect may be beneficial in counterbalancing or reversing the arteriolar vasoconstriction that settles within hours following BRVO, with subsequent improvement of arteriolar blood flow.