The potential role of adenosine in regulating blood flow in the eye

Blood flow in the eye has shown a remarkable ability to autoregulate regardless of intraocular pressure, perfusion pressure or alterations in arterial pressure. This study investigates the possibility that adenosine may play a role in regulating ocular blood flow. Ocular blood flow was measured using radio-labelled 85Sr microsphere and laser Doppler techniques. When two adenosine uptake inhibitors, dipyridamole and papaverine were injected intravitreally, the ocular blood flow increased in all ocular tissues tested: iris, iris root-ciliary body, retina and choroid. This increase in blood flow was blocked by the addition of the adenosine antagonist, 8-phenyltheophylline. The increase in flow produced by dipyridamole continued for up to an hour after administration. The increase in blood flow in individual ocular tissues does not appear to be due to shunting (ie. redistribution) of flow because total blood flow to the eye increased but the percent total flow to each individual tissue remained near control values.