Platelet 5-HT uptake in delusional and nondelusional depressions.

Platelet 5-hydroxytryptamine (5-HT) uptake was measured in a group of 28 endogenously depressed patients, at three points during the day, before, during and after treatment. It was also measured in 20 controls at the same three times. Uptake rates varied in control subjects in a manner consistent with the presence of a circadian rhythm in uptake. This variation was absent in depressed subjects. Deluded and nondeluded depressives showed a similar absence of variation but differed in the absolute values for their uptake rates. In particular deluded depressives did not show the lowering of platelet uptake rates, which has been widely reported for endogenous depression. This difference between the two groups was maintained after treatment was started but was not present after clinical recovery, suggesting a state-rather than trait-dependent marker. These differences between deluded and nondeluded depressives have implications for the investigation of platelet 5-HT uptake in other psychiatric illnesses.