Ischemia-reperfusion injury to the rat retina was induced by raising the intraocular pressure above the systolic blood pressure for 45 minutes, followed by reperfusion for 3 days. This insult caused a reduction of the b-wave of the electroretinogram (54% +/- 5%, n = 23) relative to the contralateral control retina, an expression of
glial fibrillary acidic protein (GFAP) in the Müller cells, and an alteration in the "staining" pattern of the
calretinin immunoreactivity. The normal two to three bands of
calretinin immunoreactivity in the inner plexiform layer appeared as a single band. Elevation of the intraocular pressure for 60 minutes, followed by reperfusion of 2 weeks, caused a 40% reduction in the thickness of the inner nuclear and plexiform layers. No statistically significant changes in the other
retinal layers were recorded.
RESULTS: When the
adenosine deaminase inhibitor erythro-9-(2-hydroxyl-3-nonyl)adenine (
EHNA) was injected into the eye just before
ischemia, the
ischemia-reperfusion changes in the b-wave and
calretinin immunoreactivity were largely prevented. Similar results were observed when the
adenosine A1 receptor agonist, R-N6-(2-phenylisopropyl)adenosine (R-PLA), was administered intraperitoneally just before
ischemia. Injection of
adenosine deaminase into the eye before
ischemia seemed to potentiate the
ischemia-reperfusion effect because the reduction of the b-wave was almost complete (8% +/- 4%, n = 6). The
ischemia-reperfusion-induced expression of GFAP in the Müller cells was not reduced by any of the adenosinergic agents tested. This suggests that GFAP expression in the Müller cells is not related to a reduction in the b-wave. An injection of
EHNA into the eye before
ischemia reduced the thinning of the inner plexiform and nuclear
retinal layers so that no significant difference between them and the control retinas existed. However, an injection of
R-PIA just before
ischemia did not reduce the thinning of the
retinal layers in a statistically significant way, possibly because the
R-PIA protective effect is less than that of
EHNA and is difficult to detect when thickness of the
retinal layers is measured. It may be necessary to use higher concentrations of
R-PIA to observe a protective effect.
CONCLUSIONS: