Paradoxical enhancement of the ERG c-wave by a small dose of sodium iodate.

The early effects of sodium iodate (NaIO3) on the ERG c- and b-waves were studied in rabbits. When 30 mg NaIO3/kg body weight was administered intravenously, the c-wave amplitude decreased and was replaced by a potential of opposite polarity. However, the administration of 20 mg/kg of NaIO3 enhanced the c-wave remarkably. Twenty min after administration, the mean c-wave amplitude significantly increased (P less than 0.001) to 211 +/- 6.2% of the pre-administration amplitude, whereas that of the control was 108 +/- 13.0%. The b-wave amplitude showed no significant changes. When 10 mg/kg of NaIO3 was administered, the enhancement of the c-wave was not remarkable. These effects were similar in both pigmented and albino rabbits. A lower blood concentration of NaIO3 applied to the basal side of the retinal pigment epithelium (RPE) may initially affect only the basal membrane of the RPE resulting in the decrease in the basal membrane resistance (Rba). This would explain the transient increase in the c-wave amplitude with 20 mg NaIO3/kg.