The Effects of Naloxone on Retinal Ischemia in Rats

The efficacy of naloxone (NL), a broad spectrum opioid antagonist, on retinal ischemia, was evaluated in a rat model of retinal ischemia with histopathologic and morphometric criteria. Two intraperitoneal injections of naloxone 3 mg/kg given immediately and 6 hr after reperfusion showed beneficial effects to the retina as evaluated at 2, 7, and 14 days after reperfusion. Morphologically, the naloxone-treated group showed better-preserved ganglion cells, nerve fiber layer, and inner nuclear layer. Morphometrically, in the treated groups, inner retinal thickness at all three time points and ganglion cell counts at 7 days showed higher values than vehicle controls. This beneficial effect of naloxone was dose-dependent with a minimal effective total dose of 6 mg/kg. A possible role of opiate receptors in retinal ischemia is suggested.