Mannitol, dextromethorphan, and catalase minimize ischemic damage to retinal pigment epithelium and retina
L. Y. Gupta and M. F. Marmor
Department of Ophthalmology, Stanford University School of Medicine, Calif. 94305-5308.
We studied the recovery of retinal pigment epithelium and retinal function
after 80 minutes of pressure-induced ischemia in rabbits. Just before
restoring circulation, we gave intravenous mannitol (an osmotic agent and
free-radical scavenger), dextromethorphan (an N-methyl-D-aspartate receptor
antagonist), or catalase (an antioxidant enzyme). Mannitol has not
previously been shown to be protective for retinal or retinal pigment
epithelial ischemia. At 24 hours after reperfusion, the electroretinogram
b-wave was reduced to 37% of preischemic amplitude in untreated eyes, but
it recovered to 67% to 80% after treatment with all three agents. The
c-wave was replaced by a negative slow PIII response in control eyes and in
seven of 12 catalase-treated eyes, but it recovered by 58% to 82% in the
remaining catalase-treated eyes and all the mannitol- and
dextromethorphan-treated eyes. Histologic examination confirmed that
retinal pigment epithelium as well as retina had been damaged by the
ischemia. The effects of mannitol seem of special interest, since the drug
has a dual mechanism of action and is clinically available.
