The use of brain digoxin concentrations to confirm blood digoxin concentrations.

Recent research suggests that the cardiotoxic as well as the neurotoxic effects of digitalis may be mediated by the central nervous system. Therefore brain regions implicated in the genesis of cardiac rhythm disorders were assayed for digoxin. An 125I-labeled radioimmunoassay was used to determine blood and tissue digoxin concentrations. Digoxin was found in the optic tract and optic chiasm in each of four persons who had been taking digoxin regularly. Digoxin is apparently concentrated from blood by the choroid plexus of the fourth ventricle but not by the choroid plexus of the lateral ventricle. However, digoxin was present in the area postrema and nucleus of the vagus only in the two digoxin overdose cases. Digoxin was not detected in any of the other brain regions analyzed. The presence of digoxin in the area postrema (the chemoreceptor trigger zone) and the nucleus of the vagus in the toxic but not in the therapeutic cases suggests a mechanism for the emesis and cardiac arrest brought about by digoxin toxicity in humans. The digoxin content of the medulla, especially the surface of the medulla under the obex, may be useful in confirmation of elevated blood digoxin concentrations.