A transient reduction in parasympathetic and symptathetic activity has been demonstrated during stepwise exposure to high altitude. There are few studies assessing the effects of altitude on serotonin metabolism. Personal anecdotes suggest that ascent to high altitude can cause mood changes such as depression and apathy.
In the present study 12 healthy subjects were examined during stepwise exposure to high altitude. The objective of the study was to test the hypothesis of a temporary reduction in serotonin and its relation to SaO2 during ascent.
Serum serotonin, plasma cathecolamines, oxygen saturation (SaO2), pulse and BP were assessed at 2850 m, 3350 m, 4300 m and 4900 m. Data are mean ± SEM. Compared with baseline, serotonin decreased significantly at 2850moh (Baseline: 196,5ng/ml ± 19,6, T1: 151,8ng/ml ± 12,76, p=0,024). It then increased further after exposure to higher altitudes. Serum serotonin correlated with oxygen saturation at 2850 m (r=0,704, p=0,011). Furthermore, the oxygen saturation at 2850 m correlated with the values of serotonin at 4300 m (r= 0,736, p=0,006) and 4900 m (r=0,709, p=0,022). Noradrenaline also decreased significantly from baseline to 2850 m (233,1 pmol L-1 ± 28,8 til 161,73 pmol L-1± 13,4, p=0,011) before it increased to at the higher altitudes.
We conclude that there is a transient reduction in serotonin during stepwise exposure to high altitude and that the initial hypoxia is related to the oxygen saturation.