Serotonin uptake in blood platelets and the dexamethasone suppression test in depressed patients

Two putative biological markers of some forms of depressive illness, the dexamethasone suppression test (DST) and the Vmax of serotonin (5-hydroxytryptamine, 5-HT) uptake in blood platelets, were studied in 40 unipolar, bipolar, and schizoaffective depressed patients. The Vmax levels in those whose cortisol levels suppressed normally after dexamethasone (n = 25) were not significantly different from those of the nonsuppressors (n = 15). When a criterion of Vmax greater than or equal to 8.5 pmoles/10(7) platelets/minute of 14C-5-HT uptake was used as the lower limit of normal, 18 patients had Vmax values lower than normal, only four of whom were nonsuppressors. There was a tendency for the incidence of lower than normal Vmax levels in nonsuppressors (4/15, 26.7%) to be less than that of the suppressors (14/25, 56.0%). These results suggest that the two abnormalities are independent of each other but tend to support the hypothesis that decreased Vmax may be an adaptive response which restores serotonergic function to normal. Twenty-nine of the 40 patients (72.5%) had one or both abnormalities, a finding which suggests that determination of both parameters would significantly increase the proportion of depressed patients who could be diagnosed by these biological tests.