Local Modulation of Retinal Vein Tone

Abstract

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 À12 -10 À8 M) or adenosine (10 À10 -10 À4 M). Adenosine (10 À6 M) was also applied on veins during preconstriction with endothelin-1 (10 À8 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 À11 M and above. At 10 À8 M the maximal endothelin-1-induced contractions were to 70.2 6 2.1% of baseline. Adenosine produced a dose-dependent dilation reaching 113.0 6 2.4% at 10 À4 M. Adenosine (10 À6 M) induced a significant dilation in endothelin-1 (10 À8 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.

Glial Cell Contribution to Basal Vessel Diameter and Pressure-Initiated Vascular Responses in Rat Retina

“…However, it has been shown that retinal veins have a rich coat of glial cells. 25 Yu et al 17 recently showed that ET-1 and adenosine could effectively induce vasoconstriction and vasodilation in porcine retinal veins without any identifiable smooth muscle cells (SMCs). Thus, the removal of glial activity on the retinal vein via LAA may account for the increased venous diameter and suggest the possibility that glial cells are able to produce a vasomotor effect independent of SMCs.…”

“…16 A recent study provides evidence that retinal veins without identifiable smooth muscle cells can be modulated by vasoconstricting and vasodilating agents. 17 Thus, there is growing evidence that retinal veins are under some form of local autoregulation.…”

Apoptosis regulates endothelial cell number and capillary vessel diameter but not vessel regression during retinal angiogenesis

“…In adult retinas, arteries and veins are both covered in smooth muscle (Ehling et al, 2013), and these may be more effective at regulating vessel diameter than the pericytes covering the capillaries. Retinal vasculature is subject to metabolic regulation (Pournaras et al, 2008), and although the smooth muscle layer around retinal veins is thinner and less organised than arteries, there is evidence that it is capable of vasoconstriction (Yu et al, 2016). The functional consequence of increased EC density and capillary diameter on retinal vascular function and metabolic regulation in particular deserves further investigation.…”

Constriction of Retinal Venules to Endothelin-1: Obligatory Roles of ETA Receptors, Extracellular Calcium Entry, and Rho Kinase

“…A recent report has shown that isolated porcine retinal veins are reactive to local vasoactive factors such as vasodilator adenosine and vasoconstrictor endothelin-1 (ET-1). 9 It is unclear, however, whether smaller upstream venules exhibit similar reactivity, especially vasoconstriction, which dictates not only blood drainage but also capillary pressure and fluid exchange.…”