Platelet serotonin uptake in drug-naïve depressive patients before and after treatment with citalopram

We investigated the kinetic parameters of serotonin (5-HT) uptake into platelets in a group of 26 drug-naïve patients suffering from major depression before and after 3–7 weeks of treatment with citalopram. The degree of depression was rated using the Hamilton Depression Rating Scale (HDRS). The 5-HT uptake characteristics in untreated depressive patients were not significantly different from those of normal subjects. The apparent Michaelis constant (KM) was significantly increased, the apparent maximal velocity (Vmax) was not different from baseline, and the uptake efficiency (Vmax / KM) was significantly decreased after citalopram treatment. A significantly positive correlation between KM and Vmax was found in all groups. There was a significantly lower Vmax and Vmax / KM in the female compared with the male depressed patients before citalopram treatment; a hypothesis was supported that lowered 5-HT uptake may reflect a gender-linked vulnerability to a serotonin-related depression. A significant negative correlation between 5-HT uptake efficiency and the initial HDRS score suggests that platelet 5-HT uptake can be used as a marker of effective depressive disorder pharmacotherapy. The initial severity of depression was significantly negatively correlated with Vmax, which supported a hypothesis that the initial severity of depressive disorder could be related to the lower Vmax.