Altered serotonin uptake kinetics in multiple sclerosis.

Platelet serotonin uptake was studied in 20 patients with multiple sclerosis (MS) in acute relapse and in 20 age- and sex-matched controls. While there was no difference in the maximum velocity of the uptake, Michaelis constants were significantly higher and correlated positively with the Disability Status Scale score. The results suggest a competitive block of the serotonin uptake sites in platelets of MS patients.