EFFECTS OF EXPERIMENTALLY-INDUCED ISCHEMIA ON DOPAMINE METABOLISM IN RABBIT RETINA

Purpose. To determine the role of dopamine in experimentally induced r etinal ischemia. Experiment 1 was designed to study the effects of isc hemic levels on dopamine (DA) metabolism. Experiment 2 evaluated the e ffects of ischemic duration on DA metabolism. The effects of recircula tion time after ischemia on DA metabolism were investigated in experim ent 3. Methods. Ischemia was produced by raising intraocular pressure (IOP) in rabbits. Three levels of ischemia were used-level A, level B, and level C-representing 50%, 75%, and 100%, respectively, of the IOP necessary to produce total ischemia. Retinal levels of DA and its mai n metabolites, homovanillic acid (HVA) and 3,4-dihydroxyphenylacetic a cid (DOPAC), were measured by high-performance liquid chromatography w ith electrochemical detection. Results. Experiment 1 showed that at is chemic level B, DA contents were significantly reduced, but neither DO PAC nor HVA concentrations were altered. The reductions of retinal DA, DOPAC, and HVA concentrations were seen at level C without altering t he ratio index. Level A ischemia did not alter DA metabolism. In exper iment 2, significant reductions in DA, DOPAC, and HVA concentrations w ere found at both 30 and 60 minutes in the ischemic group, whereas the ratio DOPAC/DA and (HVA + DOPAC)/DA were significantly decreased only in the 60-minute ischemic group. Five-minute total ischemia did not a lter DA metabolism. In experiment 3, concentrations of DA were still s ignificantly decreased at 30 minutes of recirculation after ischemia, but DOPAC and HVA levels were back to normal. However, the ratios of D OPAC/DA, HVA/DA, and (HVA + DOPAC)/DA were significantly elevated. Aft er 90 and 240 minutes of recirculation, retinal DA contents had return ed to normal values, but DOPAC and HVA concentrations as well as all r atio indices of DA metabolism were still enhanced. Conclusion. Dopamin e metabolism is altered during and after retinal ischemia. Dopamine ma y play a contributing role in ischemia.