Increases in platelet 5HT uptake rates following treatment with "uptake inhibiting" drugs

A kinetic analysis of 5HT uptake into platelets and its inhibition by antidepressants is the most commonly used method of assessing the effects of antidepressants on 5HT uptake in humans. This study suggests that there is a naturally occurring variation in the uptake rates for 5HT into platelets, consistent with the presence of a circadian rhythm in uptake. There appears to be a derangement of this variation in depressed patients, which is reversed by effective treatment. Antidepressants may have effects both at the 5HT transport site and on the overall degree of variation. In view of this variation and its disruption in depression, it is suggested that measurement of the effects of "uptake inhibiting" drugs in depressed patients may yield different results to those obtained from controls. This difference is most apparent when uptake is measured at several time points. Furthermore, results from in vitro and ex vivo assays may yield distinctly different findings.