Long-term effect of lithium on the uptake of 5-hydroxytryptamine by human platelets

1 The content, uptake and storage of 5-hydroxytryptamine (5-HT) in platelets were determined in eight manic-depressive patients not on lithium (Li); in ten manic-depressive patients on Li; and in ten apparently normal persons as controls. 2 Platelets from the patients, whether or not on Li, contained less 5-HT than platelets from normal people. 3 5-HT uptake and storage by platelets from untreated patients were significantly lower than those of control subjects. 4 When patients had been on Li for 3 months or longer the diminished uptake and storage of 5-HT by their platelets were more than fully reversed. 5 Li added to platelet-rich plasma in vitro had no effect on the uptake of 5-HT by platelets.