The dynamics of changes in epinephrine (E), norepinephrine (NE), dopamine (DA), serotonin (5-HT) and its metabolite 5-HIAA in the duodenal and iliac wall was studied in the initial period of support unloading (the "dry" immersion method) and general low frequency vibration (LFV). It was found that 15-min unloading led to a sharp increase in 5-HT and DA in the duodenum, accompanied by an elevation in total electrical activity of smooth muscles, to a decrease in E, NE, and DA and, in contrast, to an increase in 5-HT and 5-HIAA in the ileum. Normalization of monoamine metabolism observed 2 h after the beginning of the unload 4 hour later was followed by inactivation of duodenal serotoninergic structures and iliac adrenergic structures. The LFV induced mostly the opposite response, decreasing 5-HT in the duodenum with accumulation of E and NE in it, and a more marked activation of inhibitory adrenergic innervation of the ileum.