Effects of lithium carbonate on serotonin uptake in rat blood platelets.

1. Lithium carbonate administration to male rats for 1 to 4 weeks increased the affinity of platelet serotonin (5-HT) uptake (decreased Km) and decreased the rate of 5-HT uptake (Vmax) when the serum lithium levels were 0.5 meq/1 to 0.65 meq/l. When the serum levels were increased further to 1 meq/1, Vmax decreased further, without additional change in Km. 2. No effect on the kinetics of 5-HT uptake was observed when serum lithium levels were at 0.4 meq/1 or below. 3. Addition of lithium carbonate in vitro (1 meq/1) had no effect on the Km and Vmax of rat platelet 5-HT uptake. 4. The possible mechanism of the inhibitory effect of lithium treatment on platelet 5-HT uptake is discussed.