Effect of P2X7 receptor activation on the retinal vasculature of non–diabetic and diabetic rabbits

Abstract

Abstract: : Purpose:We previously reported that retinal microvasculature becomes more vulnerable to cell death initiated via P2X₇ receptors within 2 weeks after the onset of streptozotocin–induced diabetes (IOVS: in press). Here, we tested whether activation of P2X₇ receptors alters retinal blood flow in diabetic rabbits. Methods:We used normal or diabetic rabbits. Diabetes was induced by alloxan (80 mg/kg i.v.). We performed immunohistochemistry in a normal rabbit eye using P2X₇ receptor antibodies. Retinal blood flow in the medullary area was measured using laser speckle flowgraphy developed in Japan (Tamaki et al, IOVS, 1994). Visual function was assessed by electroretinogram (ERG). Apoptosis was examined by the TUNEL assay. Results:Vessels in the retina and optic nerve head (ONH) were immunoreactive to P2X₇ receptor antibodies. When assayed 24 h after intravitreal injection of 150 nmol BzATP, a P2X₇ agonist, the retinal circulation in normal rabbits was reduced by ∼30%; this reduction continued for at least 2 weeks. Apoptotic cells were detected in the vascular cells of the retina and ONH of non–diabetic rabbits injected with BzATP though no apoptotic cells were found in those injected with the vehicle. In contrast, 50 nmol BzATP was without effect on blood flow, apoptosis. In rabbits made diabetic by alloxan, the retinal blood flow significantly decreased until 3 days and recovered to the baseline level. At 2 weeks after alloxan treatment, the injection of 50 nmol BzATP reduced the blood flow by ∼30% for at least 2 weeks. Also, the amplitude of ERG oscillatory potentials was decreased in eyes of diabetic rabbits injected with 50 nmol BzATP. Conclusions:Activation of P2X₇ receptors reduced the retinal circulation in rabbits. Soon after the onset of alloxan–induced diabetes, the circulation becomes more vulnerable to reduction initiated via P2X₇ receptors. Our findings support the idea that the retinal circulation disorder accelerated by activation of P2X₇ receptors may be involved in the mechanism by which diabetic retinopathy progresses.

Keywords: blood supply • apoptosis/cell death • electrophysiology: non–clinical