Dopamine uptake by platelets in hepatic encephalopathy; evidence for a possible depletion of brain dopamine.

A decrease in H3-dopamine uptake was demonstrated in the blood platelets of 22 hepatic encephalopathy (HE) patients when compared to that of patients with liver cirrhosis, but without HE, and controls. There was a direct correlation between the stage of HE and the decrease in H3-dopamine uptake. As blood platelets have characteristics similar to neurons which contain amines, they have been proposed as a model for the study of amine metabolism in neurological, as well as liver diseases. A defective dopamine uptake by the HE platelets suggests that a similar biochemical derangement is, also, present in the nerve cells of the dopaminergic system. This could account for the clinical evidence of extrapiramidal dysfunction and the arousal effect of levodopa in HE. Platelets from 10 cirrhosis, but HE-free, patients had a dopamine uptake which was intermediate between the HE patients and controls. When octopamine was added at the same concentrations as in serum of HE patients, the blood platelets from five controls showed a decrease in dopamine uptake proportional to the concentration of octopamine added. Octopamine may impair dopamine uptake by platelets from HE patients.