Effect of lithium carbonate on serotonin uptake in blood platelets of patients with affective disorders.

Lithium carbonate treatment for 2-3 weeks produced a significant decrease in the maximum velocity (Vmax) of serotonin (5-HT) uptake, a measure of the number of 5-HT uptake sites in blood platelets from bipolar patients. The decrease was more pronounced in bipolar manic patients than bipolar depressed patients. There was no significant affect on the affinity for 5-HT (Km) of the uptake sites in the platelets of manic or depressed bipolar patients although Km did decrease (indicating increased affinity) in the majority of subjects from both groups of patients. However, lithium treatment of at least 1 year duration was associated with significant increases in Vmax without affecting Km. Lithium in vitro, at concentrations up to 1 mM, had no effect on the Km or Vmax of 5-HT uptake in blood platelets of normal controls. The possible mechanisms of the inhibitory and stimulatory effect of lithium carbonate treatment on platelet 5-HT uptake are discussed.