Purpose: The endothelins are potent vasoactive peptides. This study was performed to characterize the in vivo effects of the endothelin peptides on the retinal circulation in nondiabetic and diabetic rats.
Methods: The video fluorescein angiography methodology was used to quantitate retinal hemodynamic responses to endothelin-1 (ET-1) and endothelin-3 (ET-3) in rats. A total of 99 rats were used for these experiments. Video fluorescein angiography recordings were performed before and at different times after intravitreal injection of different concentrations of ET-1 and ET-3 in nondiabetic and diabetic rats. Vascular diameters and retinal circulation times were determined using computer-assisted image analysis of the recorded angiograms.
Results: The maximal response to ET-1 was observed at 15 minutes after intravitreal injection and was maintained for as long as 30 minutes after injection. Subsequent data measured at 15 minutes after intravitreal injection showed significant prolongation of retinal circulation times and retinal artery constriction. For example, at a concentration of 10(-7) M, the retinal circulation time increased by 270% +/- 121% of the baseline value. In contrast, 10(-7) M ET-3 injection showed a 52% +/- 29.5% increase in circulation time compared to baseline. In diabetic animals, 10(-7) M ET-1 injection showed a blunted response (only 26% +/- 8% of baseline) compared to the same ET-1 injected concentration in nondiabetic rats.
Conclusions: The rat retinal circulation shows a pronounced retinal response to ET-1 intravitreal injection. The response to ET-3 is significantly less than it is to ET-1, and in diabetic animals there was also a significant blunting of the retinal response to ET-1. The blunted response to ET-3 is consistent with the lower affinity of retinal vessel ET-1 receptors to ET-3. The blunted ET-1 response in diabetic rats is consistent with previously reported results, demonstrating resistance to ET-1 action in retinal pericytes exposed to high glucose.