Platelet-5HT uptake and gastrointestinal symptoms in patients suffering from major depression

The objective of this study was to determine whether the presence of gastrointestinal symptoms, as defined by item 12 of Hamilton-Rating-Scale for Depression, is related to kinetic characteristics of platelet-5HT uptake in patients with major depression. The clinical picture of depression in patients with severe form of appetite loss with difficulties of eating (item 12 = 2) and weight loss was characterized by the combination of depressed mood with somatic symptoms of anxiety, sleep disturbances, decreased activity and the presence of nausea. The high frequency of relatively low Vmax and Km of 5HT uptake in this group (n = 12), all in the lower range of controls, resulted in significantly lower mean values compared with patients without gastrointestinal symptoms (n = 16; item 12 = 0) or 57 healthy subjects (Vmax = 1.36 +/- 0.27 vs. 2.14 +/- 0.85 vs. 2.05 +/- 0.74 nMol 5HT/10(9)plat.x min; Km = 382 +/- 68 vs. 467 +/- 94 vs. 492 +/- 123 nM respectively). Although our finding needs confirmation, it seems that in the research for serotonergic mechanisms in major depression, it makes sense to look at depressed patients with or without somatic symptoms separately. Based on findings in 5HT transporter knock-out mice (J. Neurosci. 15 (2001) 6348), we assume that the low apparent Vmax of platelet-5HT uptake reflects the low expression of 5HT transporter not only in platelets, but also in the gut mucosa and enteric serotonergic neurons, which probably increases the risk of typical gastrointestinal symptoms such as appetite loss and nausea occurring in some depressed patients.