Angiotensin II binding receptors in retinal and optic nerve head blood vessels. An autoradiographic approach

Angiotensin II (AII) binding sites were identified in cross-sections of the cat retinal and optic nerve vasculatures. The authors used 3H-AII and 125I-saralasin, an agonist and a high-affinity antagonist of AII receptors, respectively, to generate light microscopy autoradiograms in resin-embedded tissues. With both radioligands the presence of AII binding sites was confirmed in retinal arterioles but not in the veins or capillaries of the retina. Additionally the presence of such binding sites in the capillaries of the optic nerve head was shown. These results support the hypothesis that microvascular tone and perhaps autoregulatory responses of optic nerve capillaries might be influenced by vasoactive substances, such as AII, either leaking from the choroid or locally synthetized.