Changes in electroretinogram and serum potassium during L-DOPA treatment in parkinsonism

The relationship of L-DOPA plasma level, parameters of ERG and severity of extrapyramidal symptoms after a single dose of L-DOPA was investigated in 11 patients suffering from parkinsonism of idiopathic or arteriosclerotic origin. After a drug-free night, each patient received his/her usual morning dose of L-DOPA. In the subsequent 3 h, the ERG recordings, blood levels and clinical ratings of extrapyramidal symptoms significantly dropped after a delay of 60 min in relation to the occurrence of the peak plasma L DOPA level. The initial "b" wave amplitudes as well as initial serum potassium values were abnormally high. There was a statistically significant correlation between the decrease of "b" wave amplitude (delta "b") and the potassium "normalization index" (i.e. the ratio between the observed decrease of serum potassium and the pretreatment difference from the middle normal potassium value). A definite interpretation of the data cannot be provided until more knowledge about the origin of "b" wave of ERG is available. It can be concluded tentatively that dopaminergic processes influence electrophysiological reactivity of the retina.