Adrenergic alpha 1 and alpha 2 binding sites are present in bovine retinal blood vessels.

Bovine retinal vessels have sites that specifically bind 3H-p-aminoclonidine (3H-PAC) with an apparent dissociation constant of 0.12 nM and a capacity of binding of 0.15 pmol/g. In addition, these vessels have 3H-prazosin binding sites bearing a dissociation constant of 5 nM and a binding capacity of 5 pmol/g. To understand the implications for retina-optic nerve vascular physiology and pathophysiology, studies of the exact location of the binding sites, the bioavailability of the adrenergic agonists, and the physiological responses to receptor stimulation in both normal and pathological states are required. The neural elements of the retina also have binding sites for 3H-PAC with an apparent dissociation constant of 0.38 nM in larger quantities (6.7 pmol/g tissue) than in the vascular elements. There are also binding sites for 3H-prazosin in a lower amount than in the vascular fraction (3 pmol/g tissue) with a dissociation constant of 2.4 nM. These sites are presumably related to the use of norepinephrine and dopamine as neurotransmitters by retinal neurons.