5-Hydroxytryptamine andcholera secretion: a histochemical andphysiological study incats

SUMMARY Theeffect ofcholera toxin on thecontentof5-hydroxytryptamine (5-HT) inthe enterochromaffin cells ofthecatsmall intestine was estimated bycytofluorimetry ofindividual enterochromaffin cells atvarying times after exposing theintestinal mucosa tothetoxin. The observed changes in5-HTlevels intheenterochromaffin cells were correlated withthe simultaneously measured rateofnetfluid transport acrosstheintestinal epithelium. Intestinal segments exposed tocholera toxin showed a statistically significant decrease in5-HTlevels of enterochromaffin cells compared withsegments exposed toheat-inactivated cholera toxin. A goodcorrelation (r=0.73) was foundbetween relative 5-HTfluorescence inenterochromaffin cells andnetfluid transport acrosstheintestinal epithelium. Thus, adiminished 5-HTcontent was associated witha decreased rateoffluid absorption or an increased rateofsecretion. A hypothesis ispresented forexplaining thepossible roleoftheenterochromaffin cells inthe pathophysiology ofcholera secretion. During thelast decade ithasbecomeincreasingly clear thatthehormonal andnervous control of gastrointestinal function isverycomplex indeed. Thenumberofhormones andhormone'candidates'" hasincreased dramatically. Theenteric nervous system, previously believed toconsist only ofadrenergic andcholinergic neurons, hasbeen showntocontain several types ofpeptidergic nerve cells, manyofwhichappear tostore oneofthe classical transmitters inaddition tothepeptide (for a recent review, seereference -2). Itmaybeassumed that gastrointestinal homones andenteric nerves not onlyplaya physiological role, butarealsoof importance inthepathophysiology ofdifferent diseases. Candidate hormones havebeeninferred in discussions ofsecretory diarrhoeas - forexample, theVerner-Morrison syndrome. Itisusually assumed, however, thatneither nervesnor hormones areofanyimportance inexplaining the severe fluid loss fromthegutseenincholera. Nevertheless, wehaverecently presented experimental evidence foraninvolvement oftheenteric