Accumulation Glycosides by in Relation to of Radioactive Cardiac Various Brain Regions the Dysrhythmogenic Effect

1 Ouabain was administered at a loading dose of 3 jg/kg followed by an infusion at a rate of 1 jig kg-1 min-' in order to produce severe dysrhythmia in dogs within 60 minutes. Similarly, digitoxin at a loading dose of 9 jg/kg followed by an infusion at a rate of 3 ,ug kg-' min-' was administered to compare its effect with that of ouabain. 2 During the 60 min experimental period, the plasma concentrations gradually rose with the continuous infusion of these drugs. However, in comparison to the 60 min plasma value of 119 ± 20 pmol/ml for ouabain and 177 + 68 pmol/ml for digitoxin, the cerebrospinal fluid (CSF) concentrations for these drugs at this time were less than 5 pmol/ml. 3 Upon termination of the experiment at 60 min it was found that kidney, liver, heart, adrenal, and the non-neural tissue in the brain such as pituitary and choroid plexus concentrated ouabain and digitoxin to give high tissue to plasma ratios. However, various neural areas of the brain (cerebellum, mesencephalon, hypothalamus, pons, and medulla) showed no preferential localization or uptake of these two glycosides. 4 Concentration of ouabain and digitoxin by the choroid plexus does not seem to affect the ionic composition of the CSF. 5 It was concluded that sampling the large areas of neural tissue listed above could provide no evidence for local accumulation of digitalis glycosides that might account for a central nervous system origin of digitalis-induced cardiac arrhythmias.