Reduced sodium absorption in the colon under serotonin is a potential factor aggravating secretory diarrhea

Background. Serotonin is a substance with a propulsive effect on the gastrointestinal tract. It stimulates the intestinal secretion of water and electrolytes, and plays an important role in the pathophysiology of secretory diarrhea. However, the influence of serotonin on intestinal absorption is very poorly understood. Objectives. This study aimed to evaluate the serotonin and selected antagonists of serotonin receptors, i.e., ondansetron (5-HT3) and GR113808 (5-HT4), on electrogenic sodium ion absorption in the colon. Materials and methods. The electrophysiologic method developed by Ussing and modified with a stimulating function on the mucosal side of the isolated colon wall was used. The influence of selected serotonergic compounds on the electrogenic transport of sodium ions under stationary conditions and mechanical stimulation was investigated. For this purpose, experiments were performed on specimens of isolated rabbit colon. Amiloride and bumetanide were used as reagents directly controlling individual ion transport. The data were analyzed using tests for paired samples (paired sample t-test, Wilcoxon signed-rank test and one-sided sign test). Results. Serotonin reduced stationary and stimulated colonic sodium absorption. The 5-HT3 receptor antagonist did not influence the studied phenomenon, while 5-HT4 antagonists acted contrary to serotonin. Conclusions. Serotonin reduces both stationary and stimulated sodium ion absorption, thus playing an important role in the pathophysiology of secretory diarrhea. The described phenomenon depends on serotonin's action on 5-HT4 receptors.