Table 1.

Stages of diabetic retinopathy and corresponding levels of ET-1

Pre-clinical diabetic retinopathy (haemodynamic and hystopathological abnormalities)	Clinical diabetic retinopathy (clinically visible lesions)	Severe diabetic retinopathy (pre-proliferative and proliferative diabetic retinopathy)
ET-1 increased	ET-1 decreased	ET-1 and ET-3 increased
Activation of ECs/pericytes and mitogenic effect on VSMCs	Reduced action on pericytes and VSMCs	Upregulation of ECs, pericytes, and VSMCs
Increased extent of microangiopathy	Capillary dilation, microaneurysms, and fluid leakage	Capillary occlusion, ischemia, and neovascularization

Actions of ET system over ECs/pericytes/VSMCs and structural changes in diabetic retinal tissue

ECs endothelial cells, ET-1 endothelin-1, ET-3 endothelin-3, VSMCs vascular smooth muscle cells