5-Hydroxytryptamine and cholera secretion: a histochemical and physiological study in cats.

The effect of cholera toxin on the content of 5-hydroxytryptamine (5-HT) in the enterochromaffin cells of the cat small intestine was estimated by cytofluorimetry of individual enterochromaffin cells at varying times after exposing the intestinal mucosa to the toxin. The observed changes in 5-HT levels in the enterochromaffin cells were correlated with the simultaneously measured rate of net fluid transport across the intestinal epithelium. Intestinal segments exposed to cholera toxin showed a statistically significant decrease in 5-HT levels of enterochromaffin cells compared with segments exposed to heat-inactivated cholera toxin. A good correlation (r = 0.73) was found between relative 5-HT fluorescence in enterochromaffin cells and net fluid transport across the intestinal epithelium. Thus, a diminished 5-HT content was associated with a decreased rate of fluid absorption or an increased rate of secretion. A hypothesis is presented for explaining the possible role of the enterochromaffin cells in the pathophysiology of cholera secretion.