Variations in platelet 5-hydroxytryptamine in control and depressed populations

Platelet 5-hydroxytryptamine uptake was measured in a group of 28 endogenously depressed patients at three points during the day, before, during and after treatment and 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. Normal variation was restored in those patients showing a clinical response, irrespective of the effects of treatment on the affinity of the uptake system. This restoration was not found in nonresponders or acutely after treatment was commenced. These findings suggest that depression is associated with a disruption of circadian rhythms, that abnormalities of platelet 5-hydroxytryptamine uptake are secondary to such a disruption and that antidepressants may act to correct this disruption.