Role of the peripheral serotoninergic system in the pathogenesis of vasovagal syncope

To evaluate the role of peripheral serotoninergic system in the pathogenesis of vasovagal syncope.

Increased central serotoninergic activity was suggested to play a role in sudden inhibition of sympathetic activity responsible for the genesis of vasovagal syncope. There is good correlation between the central serotoninergic activity and the plasma levels of serotonine.

In twenty-two patients (mean age 48 +/- 19 years, 10 men, 12 women) with suspected vasovagal syncope head-up tilt test (HUT) was performed. Passive HUT (60 degrees, 20 minutes) was followed, if negative, by nitroglycerine stimulated HUT (400 microg sublingually, 15 minutes). Blood samples were obtained at baseline (in supine position), in 5 minute, 15 minute of HUT and finally at syncope or end of the test. Plasma levels of serotonine were measured by enzyme-immunoassay (EIA) method.

HUT was positive in fifteen patients and negative in seven patients. In all HUT positive patients syncope developed after nitroglycerine stimulation. Mean duration of nitroglycerine phase was 4.8 +/- 1.2 min. In 5 min of HUT serotonine level was significantly lower in HUT positive patients HUT (102.40 +/- 43.11 vs 160.85 +/- 43.71 ng/ml, p = 0.01). At the time of syncope no significant differences were observed between HUT positive and HUT negative patients (184.26 +/- 118.72 vs 196.57 +/- 88.91 ng/ml, p = 0.40).

In patients with vasovagal syncope lower level of plasma serotonine were observed during early HUT when compared to controls. No differences in serotonin activity were observed at the time of syncope (Tab. 1, Fig. 1, Ref. 24).