Studies on the Handling of Retinotoxic Doses of Iodate in Rabbits

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Abstract
Accumulation of iodate in eye tissues and fluids as a possible explanation of the retinotoxic effect of iodate has been studied by intravenous injection of NaIO3(30 mg/kg), 125IO‐3 and 131I‐ in rabbits. 125IO‐3 was determined in fluids and tissue extracts by precipitation with BaCl2 after addition of KIO3. 125IO‐3 was rapidly broken down in blood T1/2 = 14 min.). 125IO‐3 was not present in aqueous humour, vitreous or extracts from retina, choroid + pigmentary epithelium or liver. Concentrations of 125I were comparable in blood, choroid + pigmentary epithelium and liver tissue while in vitreous and aqueous humour low concentrations of 125I were found which, however, increased gradually during 5 hrs after injection to reach levels comparable with blood levels of 125I. Retina had a low concentration of 125I. The ratio 125I/131 I (R) in blood decreases during the first 60 min. after injection followed by a slow rise. R in retina, choroid + pigmentary epithelium and liver was the same as in blood at the same time after injection. During the first 80 min. after injection R was higher in vitreous than in blood while it was lower in aqueous humour than in blood. At longer times after injection R was identical in the three fluids, The investigation has been supplemented with whole body scintigraphy of rabbits injected with NaIO3 (30 mg/kg) and 131IO‐3 or 131I‐. The reduction kinetics of IO‐3 to I‐ by some body fluids, tissues, cystein and glutathione was also studied. It is concluded that the retinotoxic effect of iodate is not due to accumulation of IO‐3 in eye tissues, but more likely to damage to biochemical mechanisms involved in the reduction of IO‐3 to.