ADRB2 and Hyperglycemia: To elucidate the involvement of β-AR-mediated signaling in cell damage that was induced by hyperglycemia, we first evaluated the mRNA levels of β1-, β2-, and β3-AR in HREC that was treated with 25 mM of HG to mimic in vitro the insult to the retinal endothelium occurring in late stage of DR.