Effects of pentagastrin and oxyphenonium on the levels of serotonin and 5-hydroxyindoleacetic acid in different parts of the digestive tract, blood and brain of rats.

In the experiments of Wistar rats it was found that pentagastrin in a dose of 0.6 microgram/kg decreased the level of serotonin and increased that of 5-HIAA in the stomach wall, and in a dose of 3 micrograms/kg it had no effect on these parameters, while in a dose of 6 micrograms/kg it decreased only the serotonin level. Oxyphenonium 0.5 mg/kg increased only the 5-HIAA level in the stomach, and in a dose of 5 mg/kg it decreased also the level of serotonin, In the duodenum these substances remained unchanged after pentagastrin administration, but oxyphenonium 5 mg/kg caused a significant fall of serotonin and increase of 5-HIAA, which was associated with a decrease in the number of enterochromaffin cells. In the small intestine pentagastrin 0.6 micrograms/kg increased the serotonin level and decreased that of 5-HIAA, in a dose of 3 micrograms/kg it decreased only the 5-HIAA level, and in the 6 micrograms/kg dose it had no effect on the levels of these substances. Oxyphenonium increased only the intestinal 5-HIAA level but only when administered in a dose of 5 mg/kg. In the brain both higher doses of pentagastrin decreased the serotonin level, and all three doses raised significantly the 5-HIAA level. Oxyphenonium in the higher dose raised the brain serotonin level, but was without effect on the 5-HIAA level. The blood serotonin level was not changed by pentagastrin and oxyphenonium.