Effect of serotonin on active electrolyte transport in rabbit ileum, gallbladder, and colon

The effect of serotonin on active electrolyte transport was evaluated in vitro in epithelial sheets of rabbit ileum, gallbladder, and colon under short-circuited conditions. Serotonin added to the serosal surface of rabbit ileum caused a dose-dependent short-lived increase in short-circuit current and a more prolonged equal effect on net Na and Cl fluxes. The latter consisted primarily of inhibition of mucosal-to-serosal fluxes of both Na and Cl. In addition serosal serotonin decreased ileal Na influx from the mucosal solution into the epithelium, suggesting an effect on Na absorption. Serotonin did not alter all aspects of ileal absorptive function and did not affect glucose-dependent Na absorption. Consistent with serotonin acting by inhibiting NaCl absorption in the ileum, serotonin induced equal inhibition of net Na and Cl absorption in rabbit gallbladder (which has a linked Na and Cl absorptive process) but had no effect on rabbit colon (which lacks a linked Na and Cl absorptive process). In addition, adenosine 3',5'-cyclic monophosphate and serotonin both appeared to alter the same ileal NaCl absorptive process, since following stimulation of ileal secretion with the maximum concentration of theophylline, addition of serotonin did not cause any further effects.