EDNRA and diabetes mellitus: Because ET-1 has been shown to be responsible for the reduction of retinal blood flow during hyperoxia10,40, the observed impairment of this flow response in the present study might be explained by the diminished vascular responsiveness to ET-1, possibly due to ETAR desensitization34 in vascular smooth muscle cells41–46 and/or pericytes47 which are pre-exposed to the elevated level of ET-1 in diabetes.