Purpose: To determine whether vascular tone of isolated porcine retinal veins can be modulated by tissue-generated vasoactive factors such as endothelin-1 and adenosine. Such information may be useful in understanding the role of the retinal veins in regulating blood flow, and also provide a model for investigating new hypotheses suggesting a role for vasoactive factors in retinal vascular diseases such as retinal vein occlusion.
Methods: An isolated perfused retinal vein preparation was used for this study. Segments of porcine retinal veins were dissected, cannulated, and perfused, and their diameter was monitored during vasoactive agent application of increasing doses of endothelin-1 (10(-12)-10(-8) M) or adenosine (10(-10)-10(-4) M). Adenosine (10(-6) M) was also applied on veins during preconstriction with endothelin-1 (10(-8) M). The significance of any induced change in vessel diameter was assessed in relation to the baseline vessel diameter prior to any drug delivery.
Results: Dose-dependent vasocontractile responses were induced by endothelin-1 administration. Endothelin-1 produced a significant contraction at doses of 10-11 M and above. At 10(-8) M the maximal endothelin-1-induced contractions were to 70.2 ± 2.1% of baseline. Adenosine produced a dose-dependent dilation reaching 113.0 ± 2.4% at 10(-4) M. Adenosine (10(-6) M) induced a significant dilation in endothelin-1 (10(-8) M)-contracted vessels.
Conclusions: Porcine retinal veins can be modulated by both vasocontraction and vasodilation agents, suggesting that the retinal veins may play a regulatory role in the retinal circulation, particularly in regard to the capillary pressure upstream from the draining retinal veins. To our knowledge, this is the first study of vasoactivity in isolated perfused retinal veins, providing an opportunity to study the direct vasoactive effects of specific vasoactive agents.