Rho Kinase Mediates Retinal Vascular Permeability and Retinal Blood Flow in vivo

Abstract

Abstract: : Purpose:To evaluate whether Rho kinase, a mediator of myosin light chain phosphorylation and muscle contraction, is a regulator of retinal vascular permeability and retinal blood flow in vivo. Methods: Jugular vein catheters were implanted in 8–week old male Sprague Dawley rats 1 day prior to experimentation. Y–27632 (100uM), a selective inhibitor of Rho–associated protein kinase, or Oleoyl–L–α–lysophasphatidic acid (LPA, 20uM), a Rho kinase agonist, was administered intravitreally (10ul). After 10 minutes, fluorescein (70ul) was infused into the jugular catheter and retinal vascular permeability (RVP) was measured by vitreous fluorophotometry 45 min later. Arterio–venous peak time (proportional to mean circulation time and inversely related to retinal blood flow) was measured by dye dilution technique using a scanning laser ophthalmoscope (SLO) and rapid bolus injection of fluorescein dye (0.5ul) into the jugular vein catheter. Results: Y–27632 inhibition of Rho kinase increased RVP 203.8% (15.23+7.13au, p<0.001) as compared with BSS control (7.47+3.00 au). In contrast, Rho kinase activation by LPA reduced RVP by 48.1% (3.88+1.11 au, p<0.009) compared to BSS control. LPA decreased retinal artery diameter and increased arterio–venous peak time 76.6% (2.31+0.34 seconds, p=0.018) at 15 minutes as compared to baseline (1.77+0.15 seconds). This effect was maintained at 30 minutes (p=0.035). Y–27632 did not significantly alter arterio–venous peak time. Conclusions: Rho–Kinase activation reduces retinal vascular permeability and retinal blood flow while Rho–kinase inhibition increases RVP. These data suggest that modulation of Rho kinase may be an important regulatory mechanism underlying retinal vascular homeostais and imply that pharmacologic manipulation of Rho kinase may have therapeutic potential for conditions such as diabetic macular edema.

Keywords: diabetic retinopathy • retina • signal transduction